Hello everyone! I've noticed there isn't an in depth guide to the recommended levels of each dungeon
so I thought I'd attempt and update this guide as I go along. Hopefully I won't miss anything too important but feel free to correct me if anything is incorrect, the more accurate the better.

This will be dedicated to the recommended levels for each dungeon but I will happily answer any questions including where to find certain materials for plans. Use CTRL+F to find things faster and I hope you find this guide useful!

Quick tips before you start:

Remember to install the free DLC as it can give you new weapons and characters.
Pressing Q will allow you to skip animation in battle
Pressing space will skip through dialogue scenes (incredibly fast)
Hugging the sides of a map will allow you to avoid unwanted mobs.
There is no right way on who to have in your party, try them all and see who is best for you.
Overleveling is your best friend.

I'd also like to poll who your favourite character is so feel free to comment!

Thank you for taking the time to use this guide, have fun!

I have also completed the same guide for Re;Birth2 and Re;Birth3
http://steamproxy.com/sharedfiles/filedetails/?id=1103701573
https://steamproxy.com/sharedfiles/filedetails/?id=2386769405

All of the dungeons listed here are involved with the storyline. If you're struggling with a particular area it may be ideal to farm at another area before continuing. There will a list of suitable monsters to farm in one of the posts below.

Monsters marked with (\) have drops needed for a quest.
Monsters marked with (!) are triggered through a story event.

Warning: If you die you will be returned to the main menu, remember to regularly save and save at every savepoint mid dungeon.

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Virtua Forest - Recommended level 1 ~ 2

Dogoo
Tulip
Dogoo-Man
Boxer-X (\)

Congratulations on making it past the cutscenes and dialogue. This is the first dungeon and the easiest to clear out, there should be no worries on defeating the little guys. Some drops here can be exchanged in quests later on so feel free to collect as much as you want.

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Monster Cave - Recommended level 2 ~ 4

Ms. Clyde
Clyde
Pixelvader
Super Otaku(\)
Contracted Angel
Guard Vermin(!)
?????(!)

You will face both Guard Vermin and ????? twice, shouldn't be a problem but remember to use Compa's heal skill if necessary. You may level once or twice from both of these.

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West Wind Valley - Recommended level 5 ~ 25

Cardbird
Sunflowery
Pal Shell
Alranne
Purr4
Ancient Dragon (Dangerous)
Shoebill(\)
Huge Dogoo(\) (Add Enemies)
Hraesvelgr(!)
Black Heart(!)

I came here at level 7 and found the normal mobs incredibly easy but be careful of monsters that can turn viral. The Ancient Dragon can be seen on your map as a dangerous enemy and should not be encountered until atleast level 15. It is possible to take out both Hraesvelgr and Black Heart at level 11 though it is recommended to be at least level 15. The Huge Dogoo is recommended at 25.

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Thelad Sanctuary - Recommended level 18 ~ 35

Terits
Spider
Plum-met
Tokimeki Sister(\)
Phoenix
Boss Lizard (Add Enemies)
Galakryzer (Add Enemies)
Boss Lizard(!)
Slash Dog(!)

I recommend atleast level 18 for the first instance, this will also make the normal mobs much easier. Phoenix and Slash Dog was also defeated at level 18 with HDD switched on. Boss Lizard (Add Enemies) was defeated at level 26. To kill Galakryser at level 35 make sure to break him with either Compa's or IF's poison attacks, this way he won't regenerate his health. This fight required 3 EXE skills to kill him.

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Avenir Storage No.3 - Recommended level 21 ~ 35

Poxvader
Bit Custom(\)
Healing Dogoo
R-4
R4i-SOHC (Dangerous)
Matango(\)
Whale (Add Enemies)
Alkeid (Add Enemies)
R4i-SDHC(!)
Killachine(!)

You cannot save when you enter this dungeon and there will be many unavoidable mobs so make sure you stock up on potions. I fought these mobs at level 21 and found no problems, the dangerous monster was fought at level 35 with no problems. If you use the Add Enemies plan you can use the Whales to farm as they give 8k each, it's recommended to be level 24 when facing these. It is recommended to be 35 for Alkeid, he gives 20k+ exp so you may want to use him to farm.
The bosses for this area can dish out some damage at level 21 so keep an eye on your hp.

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MS Mountain - Recommended level 25 ~ 42

Boomerang
Apeldoom
Lightbulb Angel
WO Head
Dolphin(\) (Dangerous)
Xdog
Directionless Soldier (Add Enemies)
Pollux (Add Enemies)

At 25 you will get your first EXE skill. You will notice how powerful these are compared to regular skills so it's a good idea to build up your EXE gauge before fighting the boss. The dolphin can also be tackled at 25 but I recommend using HDD and EXE. The event is a harder variation of the normal mobs, they shouldn't dish out too much damage but they have a lot of health, concentrate on the angels first. I fought the Directionless Soldier and level 40, his hp is easy to take down with an EXE but he can dish out a bit of damage, I defeated Pollux at level 42 with two EXE skills.

You can find a CREDIT+ Plan in a hidden chest here.

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Marubaco Forest - Recommended level 29 ~ 57

Boxbird
Metal Dogoo(\)
Aluna
Turtle (Dangerous)
Land Whale(Add Enemies)
Big Pirachu(Add Enemies)
Forest Whale(!)

Here you'll find dogoo's that really like avoiding attacks so it's good if you have a lot of TEC.
I fought the tutle at level 30 and it dishes out a lot of damage but appears to target one person so make sure you keep an eye out on their hp, EXE skills make this much easier. The event monster has quite a bit of hp and dishes out a bit of damage between all party members, at level 31 Compa gets a 50% aoe heal which can be incredibly helpful here. I defeated the Land Whale at level 44 with one/two EXE skills. I recommend atleast 55 for the Pirachu, I defeated it at 57 with three EXE skills.

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Halo Mountain - Recommended level: 35 ~ 58

Radisher(\)
High Heal Dogoo
Wolf
Horsebird
Fenrir Wolf (Dangerous)
Swallowtail
Kupokitty
Obese Dogoo (Add Enemies)
Judge's Disciple(\) (Add Enemies)
Arfoire(!)

Although not necessary you may want to over level before coming here as the monsters have a fair bit of hp. The Fenrir Wolf can be taken on at level 35 but a lot of healing and EXE skills will be needed. I fought the event at level 45, she has low hp so one EXE should do the trick, she also dishes out a lot of aoe damage so make sure to spread your party out. The second event is classic Arfoire, don't worry about it. I defeated the Obese Dogoo and Judge's Disciple at level 58 with three EXE skills.

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Lowee Snowfield - Recommended Level: 47 ~ 67

Frozen Skull
Lowee Soldier
Gold Lizard
Violent Good Girl(\)
tPad
Plaid Dolphin (Dangerous)
Ice Whale (Add Enemies)
Mekidrygar (Add Enemies)
Ancient Dragon(!)

You may want to level to 50 to make this easier but it's possible at 48. I defeated the Plaid Dolphin at level 48 with two EXE skills, it targets one character so what out for their hp. The event monster was defeated at level 49 with two EXE skills. The Ice Whale was defeated easily at level 67, Mekidrygar was defeated at level 67 with several EXE skills.

You can find an EXP+ plan in an hidden chest here.
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Lowee - Recommended Level: 48

Killachine Mk-2(!)

This is just one stand alone boss that can be killed by one/two EXE skills, you have the ability to change your party before the battle.

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Warning: Before going to Avenir Storage No.4 it is recommended to unlock and pick up Donkong's Add Enemies plan from Lowee. This plan can only be collected at this point and you will not have the chance to get it until NG+

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Avenir Storage No.4 - Recommended Level: 53 ~ 73

High Bit Custom
Strange Person
Ruffian Cat
OSTT
Heavy Tank(\) (Dangerous)
Eggplant rider (Add Enemies)
Wild Pirachu (Add Enemies)
Killachine Mk-3(!)
Killachine 1.01(!)

The mobs here and vunerable to paralyse so it's good to equip one of your party with either a CD or the paralyse skill. I defeated the Heavy Tank at 54 with two EXE skills. The event was fairly easy at level 54 with one/two EXE skill(s). The Eggplant rider was defeated at level 70 with two EXE skills, I defeated the Pirachu at level 73 with four EXE skills.

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Hyrarule Snowfield - Recommended Level: 56 ~ 70

Call Boy
Cold Girl
Lowee Defense Guard
Ice Golem
King Crab (Dangerous)
Special Dogoo(Add Enemies)
Alnair(Add Enemies)
Self-Defense System(!)
Item Jammer Pod(!)
Skill Jammer Pod(!)

I fought the King Crab at level 56, it is vunerable to both Paralyse and Poison making the battle much easier to rip through (also an easy battle to get the combo master achievement). For the event make sure you take out the skill pod first as it will stop you from using your EXE skills. Once that is destroyed the rest is a piece of cake. The second event is a harder variation of mobs that can dish out a bit of damage but shouldn't be a problem. The Special Dogoo and Alnair were defeated with two EXE skills at level 70.

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Stella Plains - Recommened Level: 57 ~ 70

Call Boy
Cold Girl
Lowee Defense Guard
Ice Golem
King Crab (Dangerous)
Special Dogoo (Add Enemies)
Fake White Heart(!)

The mobs here are identical to those in the previous so you shouldn't have any problems here. The event boss should be defeated within two/three EXE skills.

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Warning: After Noire rejoins the party you can collect the Item Change, Add Enemies and Super Enemies plans for Naasne Volcano. You can then unlock Millenium Labarinth by defeating Antares in Naasne so that you can get the Add Enemies and Add Items plan for ML. If you want to do it during this play through it needs to be done before the event in Planeptune after Soulsac Cave, the Add Enemies/Items is a missable plan and you won't be able to get it again until NG+.

It is recommended to start colisseum at this point for another way to gain EXP.

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Soulsac Cave - Recommended Level: 61 ~ 75

Blue Sun
Ice Lizard
Jellyfish Dogoo
Missile Golem
Garuda (Dangerous)
Unplanned Dogoo (Add Enemies)
Undisputed God's Peon (Add Enemies)

The normal mobs here are reletively easy at level 61 but can cause paralyse. Garuda was incredibly easy at this level. The event are a variation of Missile Golems which shouldn't be a problem. I defeated Unplanned Dogoo at level 71 with two EXE skills. I defeated Undisputed God's Peon at 75, he has a high regeneration so be sure to use three similtaneous EXE skills.

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Lastation - Recommended Level: 62

Panzer(!)
CPU Breaker(!)
CPU Breaker(!)

Once again we have another stand-alone boss, it can dish out damage on squisher members but can be defeated this with two EXE skills. The first CPU Breaker is classic Arfoire, the second just needs three clonks on the head with EXE skills.

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Fantasy Zone - Recommended Level: 75 ~ 95

Plom-met
Testri
Cyberfly
Malvader
Cerberus (Dangerous)
Cyber Whale(Add Enemies)
Viral Mareshimono(Add Enemies)
Arfoire(!)
CPU Killer(!)
Overlord Momus(!)

I came here at level 80 and the mobs were incredibly easy so feel free to come here before hand. I defeated the Cerberus at level 81 with two EXE skills. With the event you can bet your buttons it's classic Arfoire. Momus was defeated at 81 with three EXE skills. Both added enemies was defeated at level 95 with two EXE skills.

Just before going here you can get the plan for Adjiten Forest Pass from Spelunker on the Map. This can be a missable dungeon so if you miss it you won't be able to get it until NG+. I suggest unlocking this dungeon and getting the Add Item/Enemy plans from Leanbox as well as getting the Uwii Ruins plan from Adjiten Forest before progressing onto the next story event.

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Ghytz Forest - Recommended Level: 80 ~ 95

Red Dogoo
Carroteer
Max(\)
Speckle
Horsebird CAW(\)
Dolichorhyochops (Dangerous)
Cat Squirrel Rider (Add Enemies)
Regulus(Add Enemies)
Fake Green Heart(!)

The enemies here deal quite a bit of damage so keep an eye out on your hp. Feel free to overlevel (look at the farming spots on one the posts below) if you want to defeat them easier. I defeated Dolichorhyochops (how do you even say that) at level 82 with two EXE skills. I fought the event at level 82 and defeated her with three EXE skills. I defeated both added enemies at level 95 with two EXE skills.

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Factory No.459 - Recommended Level: 80 ~ 95

Cass Trap
Ganglord Panther
R-4 Custom
Surpression Prototype (Dangerous)
Bundodo Old Man
Next Dimension Bit(\)
Zeta Herobo(Add Enemies)
Deus Ex Machina(Add Enemies)
Fake Black Heart(!)
Fake Black Heart(!)

The enemies here are around the same difficulty as the previous, once again feel free to overlevel if you want to. I defeated the Supression Prototype at level 82 with two EXE skills. I defeated Fake Black Heart at level 83 with one EXE skill, the second fight took two EXE skills. I defeated both added enemies at level 95 with two EXE skills.

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M-Frontier Cave - Recommended Level: 80 ~ 95

Invader
Ruin Guardian(\)
Something Tree(\)
Mega Spider
1000-Year Turtle (Dangerous)
Saint Whale(Add Enemies)
Aldebaran(Add Enemies)
Fake White Heart(!)

Once again this is the same difficulty as the previous two. The 1000-Year Turtle was defeated at 83 with two EXE skills. The levels for the added enemies will be added shortly. Fake White Heart was defeated with three EXE skills at level 83. Both added enemies was defeated at level 95 with two EXE skills.

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Neo-Geofront - Recommended Level: 80 ~ 95

Magma Boy
Magma Girl
King Boxbird
Flame Skeleton(\)
Rafflesia
Volcano Crab(\)
Bincho(\) (Dangerous)
Gebachu (Add Enemies)
Tiamat (Add Enemies)
Fake Purple Heart(!)
Fake Purple Heart(!)

At level 80 the normal mobs shouldn't be a problem, feel free to come here earlier if you wish. Bincho was defeated at 83 with two EXE skills. I defeated Fake Purple Heart at level 84 with one EXE skill, the second was defeated with three. I defeated both added enemies at level 95 with two EXE skills.

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Planeptune - Recommended Level: 85

Overlord Momus(!)
Overlord Momus(!)

I fought this event at level 85 though this can easily be tackled beforehand. I defeated it both times with three EXE skills.

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Road to Celestia: Recommended Level: 85
Demon Spider
Prince Boxbird
Lizard Knight
Skull
Lost Dragon (Dangerous)
HyperDimension Dogoo (Add Enemies)
Next-Gen Ricky (Add Enemies)
Arfoire(!)
True Arfoire(!)

Welcome to the final story dungeon! At level 85 the normal mobs should be a breeze so feel free to start here before hand if you wish. The Lost Dragon was defeated with 2 EXE skills at level 99. The first event was defeated at 99 with one EXE skill, the second was defeated with 3 EXE skills at level 99.

Endings Choice: There are two possible endings (both available in one playthrough). The 'Normal Ending' is earned by completing the game however you see fit, for the 'True Ending' you are required to have between 20%-25% shares for all four nations. For the 'True Ending' you will be against a much harder boss so you may want to aim as close to max level (99). It is recommended to save your game in two slots before the event, complete the 'Normal Ending' first, load back up the second save, complete quests until the shares are equal then complete the 'True Ending'.

These are all the dungeons that are not involved within the story line but are used within guild quests or suitable for exp/credit farming. Monsters suitable for farming will be mentioned further below. This will be updated as I go along.

Monsters marked with (\) are needed for a quest.

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Zeca Ruins No 1. - Recommended Level: 8 ~ 35

Normal Shampuru(\)
Magical Shampuru
Buff Shampuru(\)
(Dangerous) Shampuru(\)
Scary Buff Shampuru (Add Enemies)
Crazy Buff Shampuru (Add Enemies)

There are a few guild quests here but the main reason for this dungeon is to gain the Mechtro Factory dungeon plan. Normal mobs are moderatly easy to take out after level 8, dangerous at level 11. Level 25 for Scary and at least level 32 for Crazy (this one does a lot of damage).
You can find the Mechtro Factory plan here.

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Mechtro Factory - Recommended Level: 12 ~ 35

Child Wolf(\)
Heal Dogoo(\)
Lean Tuna
Cat whisker
Heavy Dragoon(\)
Nidhogg
Child Whale (Add Enemies)
Herobo (Add Enemies)

Here is our first farming spot. It is recommended to level up to 12 with the normal mobs before attacking the (Add Enemies) Child Whales. These whales give around 5k exp and can be used to grind to 30. It is recommended to fight Nidhogg at level 20 and not attempt Herobo until you are at least 35 with 3 similtaneous EXE skills.

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Ortan Fields - Recommended Level: 28 ~ 35

Bit
Delinquent Cat
Deus Man(\)
M-3
Fenrir(\) (Add Enemies)
Nurse Binder (Add Enemies)

The mobs here are fairly easy at level 28 and aren't really needed besides quest and plan materials. You can also get the plan for Toh-Kiden cave here. I fought both added enemies at level 35. Fenrir was incredibly easy and Nurse Binder has low HP but has a high heal, recommended to save two EXE bars and use two individual skills simultaneously.

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Toh-Kiden Cave - Recommended Level: 33 ~ 47

Ice boy
Ice girl
Magic Stone
Earth Golem(\)
Moulin Rouge
Elemental Dragon (Dangerous)
Replicant (Add Enemies)
Grand Dragon (Add Enemies)

I came here at level 35 and the enemies here were easy to plow through, the drops from the monsters can be used in many plans and a few quests so it's a good idea to spend a bit of time here. The Elemental Dragon can be killed with one or two EXE skill(s) at level 36. You can also get the plan to Gravidaze ruins here. I fought Replicant at level 46 and killed it with three EXE skills, the Grand Dragon was defeated at level 47 and only required one EXE skill.

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Gravidaze Ruins - Recommended Level: 40 ~ 52

Dragon Warrior
Crack Tail
Crystal Golem(\)
Old Man Deus(\)
Forest Crab (Dangerous)
Achilles (Add Enemies)
Master Dragon (Add Enemies)

Though you can attempt earlier it would be easier to start here at level 40 as mobs are beginning to have higher hp. You can find the Gunbreak Underground Cavern plan here. I fought the Forest Crab at level 46 and killed it with two EXE skills. I defeated both Master Dragon and Achilles at level 52 with 3 EXE skills, Achilles can paralyse and dish out damage so keep an eye out but is also a good source of exp giving 60k each battle.
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Gunbreak Underground Cavern - Recommended Level: 47 ~ 60

Nanovader
Numb Dogoo
Tarantula(\)
Expressive Tree
Ice Fenrir (Dangerous)
Grendel(Add Enemies)
Belgarion(Add Enemies)

The mobs here have quite a few debuffs so be keep an eye on your party, but they should be easy to take out. The Ice Fenrir can also be defeated at level 47. There are a lot of plans you can collect here, including Treasure Hunter which increases your item drop rate. Grendel was defeated with one EXE at level 60, Belgarion was defeated at level 60 with three EXE skills.

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Duty Space - Recommended Level: 50 ~ 75

Plam-met(\)
Magic Dogoo
Cuberial
Death Stalker(\)
Giant Dogoo(\) (Dangerous)
Horsebird Rider (Add Enemies)
RoboRival (Add Enemies)

I would recommend level 50 before coming here as the mobs pack a punch. You can get the Donkong Ruins plan here as well as other items. Giant Dogoo and Horsebird Rider was defeated with two/three EXE skills at level 61. I defeated RoboRival at level 80 with three EXE skills but feel free to attempt him earlier.

Warning: This is a missable plan and can only be obtained on Chapter 4 when Lowee Snowfield appears. When unlocked you should also find the Add Enemy/Items plans from the chirper.

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Donkong Ruins - Recommended Level: 50 ~ 75

High Bit
Hyena
Skeleton
Lowee High Guard
Floristan
Roc
Canopus(Add Enemies)
Grafchocolo(Add Enemies)

Here's another place you can come to at level 50, as well as being the home to another monster we can farm for exp. Roc can be defeated at level 50 with two EXE skills but keep an eye on your hp as it dishes out a lot of damage. I defeated Canopus at level 75 with two EXE skills. I defeated Grafchocolo with three/four EXE skills but he gives almost 300k exp with EXP disks. I recommend fighting him to level to 90.

It has said that the Add Enemies plan is missable. To get this plan, visit Lowee before going to Avenir Storage No.4. If you miss it you won't be able to get it until NG+

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Naasne Volcano - Recommended Level: 60 ~ 82 ~ 350

Hachibei(\)
Wood Skeleton
Wild Dog
Dragon Knight
Tortoise (Dangerous)
Antares(Add Enemies)
Peacock(Add Enemies)
Clione(Super Enemies)

Ah the Super Enemy. What is that you ask, why not touch it and find out? It requires the DLC but these are the monsters that can really give you the exp and money you've always wanted, lets wait a bit until we start because you will get utter destroyed (level will be added shortly).
The normal mobs here have quite a bit of hp so you may want to overlevel before coming here. I defeated the Tortoise at level 60 but he can deal a lot of damage and needs seveal EXE skills to kill it. I defeated Antares at level 68 with several EXE skills, I defeated Peacock at level 82 with three EXE skills. Here you can find the Kinest Range dungeon plan in a hidden treasure, it may take a few tries to find.

I defeated the Clione at 380 but found it relatively easy so feel free to take it on beforehand.

Warning: Once again this is a plan that can be missed, after Noire rejoins you can collect the Item Change, Add Enemies and Super Enemies plans from Lastation. Make sure to do this before going through the event.

By defeating Antares here you can also get the item that unlocks Millenium Labryinth, the Item and Enemy plans of this can only be gained during Chapter 6 and only if the dungeon has been unlocked. This may require you to over level, which can be helped by the colisseum (if you have the DLC).

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Millenium Labryinth - Recommended Level: 70 ~ 85 ~ 900

Prince Cardbird
EDGE
Aimable
Fairyfly
Tank Type 99 (Dangerous)
Clione (Add Enemies)
Gargoyle (Add Enemies)
Delphi Eggplant Mk-2(Super Enemies)

The normal mobs here have quite a bit of hp, you can focus rush attacks and use EXE skills to rid the mobs quicker if you want to quickly get the drops. I defeated Gargoyle at level 85 and Clione at level 86, Clione gives 2mil points each time making it an excellent way to get to max level. This can be defeated as early as level 70 with the correct equipment. I deafeated the Super at level 900 but can attempted earlier.
This dungeon and add enemy plans are incredibly easy to miss during your first run through. To get this dungeon's plans you will need to unlock the dungeon in chapter 5 by defeating Antares in Naasne Volcano. Here you need to unlock the dungeon before the Planeptune event after Soulsac Cave and receive the plans from Lastation. Here you can get the plan to Yukawa Ruins.

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Kinest Range - Recommended Level: 70 ~ 95 ~ 350

Meow
Pinky
Ms. Pinky
Paradise Avian(\)
Thunderbird(\)
Lizard King(Add Enemies)
Nemesis(Add Enemies)
Super Gebachu(Super Enemies)

The normal mobs here were incredibly easy at level 72. (THUNDERBIRDS ARE GO) was defeated with three EXE skills at level 72. Both Lizard King and Nemesis was defeated at level 95 with two EXE skills.

I defeated the Super Enemy at level 450 and he was doing 0 damage, overleveling makes it much easier but it can be defeated earlier.

Warning: This is a missable dungeon. You can get the dungeon plan from a hidden chest in Naasne Volcano, this is random so it may take a few tries. The Add Enemy/Item Plan can only be gained in chapter 6 at Leanbox after the dungeon has been unlocked otherwise you cannot unlock this until NG+.

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Yukawa Ruins - Recommended Level: 80 ~ 95 ~ 320

High Lizard
Blushing Hot Guy
A2-i
Promise Ring(\)
Ruin Dragon
Clione (Add Enemies)
Maximus Dogoous (Add Enemies)
Legacy MK-2(Super Enemies)

I recommend being at least level 80 before coming here, the mobs do a lot of damage but can be killed with one EXE if you wish to farm for drops. You can find the Zeca Ruins No.2 dungeon from an hidden chest here. The Clione and Maximus Dogoous was defeated at level 95 but can be attempted earlier to farm exp.

I defeated the Super Enemy at level 320 but it dishes out a lot of damage and requires constant healing. May want to over level before then.

Warning: This is another dungeon that can be missed if you have not gained the plan and unlocked the dungeon by chapter 6 (From Millenium Labryinth). You can then get the Add Enemy and Item Change plans from Planeptune before the Planeptune event.

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Adjiten Forest Pass: Recommended Level: 75 ~ 95 ~ 260

King Cardbird(\)
Magical Dogoo
Alune
Insatiable Tree(\)
Cyber Dolphin (Dangerous)
Deneb(Add Enemies)
Moonlight Bug(Super Enemies)

The monsters here have quite a bit of hp and the dogoos have a high heal so it's important to take them out first. You may want to wait until a higher level to make these mobs easier to plow through. You can also get the plan for Uwii Ruins here which is recommended to do so before you finish chapter 7. I defeated the Cyber Dolphin at level 82 with two EXE skills and Deneb was defeated with two EXE skills at level 95. I was level 260 when fighting the Super Enemy, you may attempt this earlier and AoE heals are incredibly useful here!

Warning: This dungeon is missable and can only be gained from Spelunker from the Chirper after Fantasy Zone has been opened. The Add Item/Enemy plans can be gained from Planeptune/Chirper before the Fantasy Zone story event.

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Uwii Ruins - Recommended Level: 85 ~ 95 ~ 500

Promise Keeper
Lowee Magical Soldier
Lost Girl
Lost Boy
Crescent Dragon(\) (Dangerous)
Trick Crown (Add Enemies)
Blue Whale (Add Enemies)
Clione (Super Enemies)

The mobs here have high healing so it's best to take those out first. I came here at level 85 but you may want to overlevel first. The Crescent dragon was killed at 85 with 3 EXE skills, he does a lot of damage though so be careful. I defeated both added enemies at 97 but they can attempted much earlier. The Clione was defeated at level 500 with constant healing needed.

Warning: This dungeon can be missed, you can gain the plan from Adjiten Forest though you need to unlock and gain the add enemy/item plan from the chirper before the last event of Chapter 7.

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Zeca Ruins No.2 - Recommended Level: 95 ~ 99 ~ 900

Orange Flower(\)
Forest Spirit
Coyote
Nue(\)
Orthrus (Dangerous)
Clione (Add Enemies)
Sirius (Add Enemies)
Sunlight Bug(Super Enemies)

Getting to the hardest dungeons you need really good equipment as the monsters here have a lot of hp and can take a beating even at level 95. You can get the Dees Snow Forest plan from here.
Both added can dish out some mighty damage but can be defeated if EXE skills are used efficently at level 99 however you will find these much easier with the extra level cap if you have DLC. It is recommended to be atleast 900, at 999 he still dished out alot of damage.

Warning: This dungeon is missable and you can only get the add enemy/item plans from the chirper during Chapter 8. You can get this plan from a hidden chest in Yukawa Ruins though it may take a few tries.

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Dees Snow Forest - Recommended Level: 95 ~ 99

Penguin
Snow Girl
Snow Boy
Snow Golem
Mega Turtle
Killachine(Add Enemies)
Epsilon(Add Enemies)

The mobs here are fairly easier than the previous, the two added enemies can be defeated with two EXE skills at 99.

Warning: Another missable as the item/enemy plan can only be gained after unlocking the dungeon in chapter 8. You can collect the last plan dungeon here: Graphic Pass.

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Graphic Pass - Recommended Level: 95 ~ 99

Tetrisi
Alfred
Old Death
Gyps
Vanargandr (Dangerous)
Dreadnaught Dogoo (Add Enemies)
Clione (Add Enemies)

Welcome to the final plan-made dungeon. I came here at level 120 but with EXE skills you can rip through these at level 99. These mobs can paralyse so watch out. I defeated Vanargandr at level 120 but should be killed with several EXE skills at 99. Added Enemies can be defeated at 99.

Warning: This plan is another that can be missed, you can collect the plan from Dees Snow Forest, the item/enemy plan can be collected just before the event from Road to Celestia, otherwise it cannot be obtained until NG+.

Here will be the recommended levels for all of the DLC dungeons. This will be how your characters will level from 99 to 999.

Noma Cave - Recommended Level: 350 ~ 450 ~ 900

Flower Fairy
Exhausted Jelly
Boxer Cat
Dogoonie
1000-Year Dolphin (Dangerous)
Clione (Add Enemies)
Cat Knight (Add Enemies)
Delphi Eggplant MK-2 (Super Enemies)

I came here at level 450 and the normal mobs were doing 0 damage to all characters so feel free to come here earlier. I recommend over leveling a little as the mobs have a lot of hp. I defeated the Clione and Cat Knight at level 480 relatively easy with a good heal. Levels for Super Enemies will be added soon.

Nights' Dimension - Recommended Level: 550 ~ 700 ~ 900

Gray Wolf
Crush's Big Brother
M-3D (Dangerous)
Suzaku (Dangerous)
Blaze Whale(Add Enemies)
Clione(Add Enemies)
Hyper Gebachu(Super Enemies)

I came here at level 550 but the enemies dish out damage quickly so you may want to overlevel before coming here. I recommend using EXE skills to kill normal mobs if you want to get it done quickly. For Suzaku and M-3D I was level 750 and killed both with two EXE guages. I also killed the added enemies at 750, feel free to attempt sooner as they did not deal any damage.

Haneda Forest - Recommended Level: 900 ~ 999

Death Boy
Death Girl
Dragonia
ASIC Remnants
Dominance Machine (Dangerous)
Procyon(Add Enemies)
Clione(Add Enemies)
True Legacy(Super Enemies)

So you want exp eh? Here's a list of recommended farming places to grind to your heart's content.
If you want even more equip your party with EXP/CRED+ Disks.

Level 12 ~ 24
Child Whales - Mechtro Factory (Add Enemies)

Level - 24 ~ 40
Whales - Avenir Storage No. 3 (Add Enemies)

Level - 40 ~ 50
Herobo - Mechtro Factory (Add Enemies)
Pollux - MS Mountain (Add Enemies)

Level 50 ~ 70
Achilles - Gravidaze Ruins (Add Enemies)
Judge's Disciple - Halo Mountain (Add Enemies)
Horsebird Rider - Duty Space (Add Enemies)

Level 70 ~ 80
Wild Pirachu - Avenir Storage No.4 (Add Enemies)
Undisputed God's Peon - Soulsac Cave (Add Enemies)
RoboRival - Duty Space (Add Enemies)

Level 80 ~ 99
RoboRival - Duty Space (Add Enemies)
Peacock - Naasne Volcano (Add Enemies)
Grafchocolo - Donkong Ruins (Add Enemies)
Clione - Millenium Labryinth (Add Enemies)

Congratulations on Max Level!

How long does it take to complete a runthrough?

It's all according to how you want to play it. If you wish to unlock all dungeons as well as take time grinding it can take up to 50 hours to complete the story, if you want to do a speed run it can take less than 20 hours. It also depends on whether you skip any dialogue or skip animation, the amount of time spent on those can really differ the pace.
I'm currently on 33 hours in Chapter 8 just before the final story dungeon.

Can you unlock all dungeons on your first runthrough?

You can though there are many that can be missed as they need to be unlocked during certain times of the game. I have wrote how to get them all within the guide (hopefully) but if you do miss one don't worry as they're not compulsary and you can always unlock it on NG+.

What is NG+?

New Game+ is when you complete the story and have the option to play again, however all your items, stats and plans are carried onto the new game. This is the only way to unlock all CPU candidates (and all achievements) as you will not have enough MB during the first run through.

Who do you use in your party?

I've seen myself switch members about 100 times during this runthrough. Currently I'm using Neptune, Rom and Blanc. I agree that Histoire is one of the best mages but I seen myself swapping her because of Rom's range of skills. I sometimes swap Neptune with Vert and Blanc with Nepgear. All depends on the situation really.

Why did you make this guide?

I have no idea why I put myself through this
When I first played this game way back when, I countlessly found myself pleading to find what levels I had to be to fight almost every monster because of the difficulty spikes in certain dungeons. I brought this during Summer Sale and I noticed a lot of people were still looking for a level guide so I thought I'd try it myself.

Will you make any other guides?
Of course! Many popular games already have really good reliable guides, but if you have a suggestion I will happily attempt to make one. I will also be starting Re;birth2 soon so I may create a guide for that.

Anything you want to know just give me a shout I'll happily answer!