Library Depths and Myouren Temple Depths are a pair of bonus dungeons available from around the one third point of postgame that were added in the Souzinengi V release of the game. As a result, they weren't available to english speaking players until now and, as a result, there's effectively no english info on the dungeon available. While they're both rather simple and can be cleared blind, there are still aspects of them (especially the boss fights) that would be very helpful to have a guide on, especially given how powerful the rewards are.

Note: Thank you to ZeldaFan024 for providing the exact rooms each enemy can be found in. You can check out their guide on that here: https://steamproxy.com/sharedfiles/filedetails/?id=3038934024

To unlock Library Depths, all you need to do is recruit all party members in postgame (with the possible exception of Akyuu) and then accept the 8 star quest "Pierce the Heavens! Scarlet Pachon." As long as the quest is active, the dungeon will appear beside the Scarlet Devil Mansion.


Note: While this dungeon can be attempted as soon as it's available, I highly recommend waiting until you've reached level 70 and at least attempted the postgame final boss. All of the fights here are rather difficult and will push you even at the initial level cap.

Library Depths is a deceptively lengthy four room dungeon. To reach the end, you need to defeat a series of five elementally themed midbosses in one go. Leaving the dungeon at any point will respawn all of the midbosses unless you've beaten all five, at which point they'll stay dead. Before entering the dungeon, make sure Patchouli has the Awakened Soul equipped to increase her bomb count by 5. Equipping it inside the dungeon will only increase her max bombs, not her current bombs, and removing it at any point will drop her max bombs again, removing any extra bombs gained from the accessory. Additionally, make sure you've obtained the +10% and +20% damage accessories for Fire, Water, Earth, Dark, and Light at minimum.

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Room A map:
Progressing even slightly into the dungeon will bring you face to face with the first midboss, the Fire Monarch. As a quick note, all five midbosses are guaranteed to ambush you, even ignoring Aya's ambush protection, and will always lead with their most powerful skill.

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Midboss 1 - Fire Monarch
Recommended party: Cirno, Marisa, Sakuya (with Almacia or Nouvelle Almacia equipped), Nitori, Patchouli in Poison Shield formation. If you aren't confident in your survivability, Marisa or Nitori can be swapped out for Alice.

The Fire Monarch will lead with Rowing Flame, a powerful single target Fire spell that deletes all of the target's Bombs. To get around this, you'll either need a lot of Quick resistance or a sacrifice. Thankfully, Cirno is only useful in this initial fight (and her damage isn't even that good anyways), so as long as you stick her in the decoy slot of Poison Shield, Rowing Flame will usually hit her instead of anyone important. (If someone else is hit, just reset. This is the first fight, so there's nothing to lose.) Afterwards, it will only use Rowing Flame again if Fire land maxes out, at which point it'll use it as its first action every turn, but that shouldn't happen as long as you're pelting it with Water attacks. During the fight proper, it'll act twice per turn and use various multi-target Fire attacks or its default Slash attack.

Marisa, Sakuya, and Nitori are free to spam their bombs in this fight, and in fact, Private Square is highly encouraged to cut its HP down quickly. Patchouli should preserve her bombs, however. Have her set Water land on the first turn and then use Ice Falchion for the rest of the fight. It should go down rather quickly.

Note: All of the midbosses drop an armor piece called the Anti-Releaser at a 5% rate. While you can run into them again as normal enemies in the Barrier Distortion, it's worth grinding out this specific fight to try and get it early as it's one of the best medium armors available at this point, especially if you come here for it earlier than intended. Just set Akyuu as your commander, and swap out Cirno and Nitori for Alice and Byakuren to increase your odds of getting the drop.

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After the Fire Monarch, you can finally encounter this dungeon's normal encounters, though I highly recommend ignoring them until you've beaten all five midbosses as they'll only drain your already limited and precious resources.

Upon progressing to the end of room A, you'll find the next midboss, the Ice Emperor.

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Midboss 2 - Ice Emperor
Recommended party: Alice, Marisa, Nitori, Mokou, Patchouli in Sunshine Lunch formation with Akyuu as commander. If you're not confident in your Water resists, use Poison Shield (with Alice as decoy) instead.

The Ice Emperor will lead with Frozen Coffin, a powerful Water spell that hits two targets and has a 100% base Paralysis rate. With Sunshine Lunch, it could end up hitting nearly any party member, but with proper Water resist, no one should die to it. If anyone is Paralyzed, have Akyuu use Healing to cure the status immediately. Afterwards, it'll only use Frozen Coffin again if Water land maxes out, at which point it'll use it as its first action every turn, but that shouldn't happen as long as you're spamming Fire attacks. During the fight proper, it'll act twice per turn and use various Water attacks, including Tsunami, which requires postive Water land, and its default Stab attack.

Alice should use Marionette Parar every turn (or Rainbow Parar if it's off cooldown), while Marisa, Nitori, and Mokou spam their bombs. Mokou is especially useful as her Fujiyama Big Eruption should do massive damage and likely even Scorch the Ice Emperor to prevent it from acting this turn, especially if the double cast procs. Patchouli should continue preserving her bombs. Set Fire land on turn one and then spam Fire Crest. Just like the Fire Monarch, it shouldn't last for very long.

Room B map:
As soon as you enter room B, climb up onto the bookshelf to hit the switch and unlock the locked gate.
Passing through the gate will lead you directly to the next midboss, the Thunder Czar.

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Midboss 3 - Thunder Czar
Recommended party: Alice, Patchouli, any three of Sanae, Litos, Satori, or Akyuu in Poison Shield formation (with Alice as decoy) and Mokou as commander.

The Thunder Czar will lead with Gibnut Zarnica, a powerful single target Thunder spell with a 100% base Death rate. If anyone dies to it, use Mokou's Phoenix's Tail to quickly revive them. Afterwards, it'll only use Gibnut Zarnica again if Thunder land maxes out, at which point it'll use it as its first action on every turn, but that shouldn't happen as long as you're spamming Earth attacks. During the fight proper, it'll attack twice per turn and use mostly single target Thunder attacks, along with Accelerate, One Million Volts, and its default Strike attack. If Accelerate is used, dispel it immediately.

Alice should use Marionette Parar every turn (or Rainbow Parar if it's off cooldown). Patchouli should continue conserving her bombs. Set Earth land on turn one and then use Diamond Cutter every turn after. Sanae should use Suwa War when its off cooldown and focus on healing and buffing the party every other turn. Satori should preserve her bombs and use Earth Javelin every turn. Akyuu should use Stone Shower whenever it's off cooldown and either Rotten Breath (unless her HP is low) or Canyon Clap every other turn. Litos should use Stone Shower and Cosmic Supercluster whenever they're off cooldown and either Energy Riot or Blaster every other turn. The lack of good Earth attacks will unfortunately prolong this fight, but it shouldn't give too much trouble as long as you're prepared.

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Progressing to the end of room B will bring you to the next midboss, the Divine Sultant.

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Midboss 4 - Divine Sultant
Recommended party: Alice, Satori, Byakuren, Patchouli, Sanae in Poison Shield formation (with Alice as decoy) with Mokou as commander
Note: Satori should learn Jesus Crush from this fight. If missed here, your only options to get it before finding these enemies again in Barrier Distortion would be to get it from either the Demiurge or the Demiurge NEO, which are both incredibly dangerous and difficult to fish for the right skills. Set Satori as the decoy instead if aiming to learn it.

The Divine Sultant will lead with Jesus Crush, a powerful Light spell that hits two targets and has a 90% Death base rate. If anyone dies to it, use Mokou's Phoenix's Tail and Sanae's Miracle Omikuji to revive them immediately. Afterwards, it'll only use Jesus Crush again if Light land maxes out, at which point it'll use it every turn, but that shouldn't happen as long as you're using enough Dark attacks. During the fight proper, it'll use various single and multi target Light attacks, including Photon Burst, which requires positive Light land, and its default Strike attack.

Alice should use Marionette Parar every turn (or Rainbow Parar if it's off cooldown). Satori should preserve her bombs and spam Dark Flare. Patchouli should use Silent Selene every turn (Artemis Necklace has too much cooldown). Byakuren should use Dark Galaxian when it's off cooldown and Dark Hole every other turn. Sanae should focus on keeping the party buffed and alive. As long as you can recover from Jesus Crush, this fight shouldn't be too much more trouble.
Note: If you want a few extra Black Diamonds without having to synthesize them, you can run the gauntlet up to this fight, and have Akyuu as your commander instead of Mokou. It'll be a little dicier, but a 50% drop rate (guaranteed if you get Byakuren's Last Word) for this valuable material is worth the effort.

Room C map:
Upon entering room C, you'll immediately encounter the last of the midboss squad, the Evil Shah.

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Midboss 5 - Evil Shah
Recommended party: Alice, Byakuren, Patchouli, Satori, Reimu in Poison Shield formation (with Alice as decoy) with Cirno as commander
Note: Satori should learn Zalam Iblis from this fight. If missed here, your only options to get it before finding these enemies again in Barrier Distortion would be to get it from either the Demiurge or the Demiurge NEO, which are both incredibly dangerous and difficult to fish for the right skills. Set Satori as the decoy instead if aiming to learn it.

The Evil Shah will lead with Zalam Iblis, a powerful single target Dark spell that has a 100% Removal base rate. Make sure your decoy has as much Quick resist as you can muster. The Problematic Silk Hat and Time-Stopping Watch are best if you have them, but otherwise, you'll need to settle for something like the Stopwatch or Platinum Jewel and Earrings of Rebellion. Cirno's commander effect should reduce the odds of Quick effects as well. If anyone dies from it, use Mokou's Phoenix's Tail, but if Removal procs, you're just down a party member. Afterwards, it'll only use Zalam Iblis again if Dark land maxes out, but that shouldn't happen as long as you keep up the assault with Light attacks. During the fight proper, it attacks twice per turn and can use various Dark attacks, including Daemonic Web, which requires positive Dark land, Mana Flare, Roar, and its default Strike attack.

Alice should use Marionette Parar (or Rainbow Parar if it's off cooldown) every turn. Reimu should set Light land immediately and then use Flawless Natural Dream, Dream Divine Spirit Strike, and Dream Spirit Needle whenever they're off cooldown and either Hyper Amulet or Great Recovery Talisman any other turn. Byakuren should use Manifestation of Mahavairocana every turn, Star Maelstrom if she drops to only a single Bomb, and White Hole once she's all out. Patchouli should use Royal Flare every turn (Starburst Inflation has too much cooldown), and Satori should use Punish the Judgment if she has it or Jesus Crush if she doesn't, then switch to Divine Gate if she runs out of Bombs. This is the hardest of the five fights, but as long as you're prepared, it should go down soon enough.

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After defeating the Evil Shah, the midbosses will no longer respawn, and you're free to leave and restock whenever you please.
From there, the Demiurge NEO is waiting at the end of the room, "blocking" the entrance into room D.

Note: It's entirely possible to squeeze past the boss and reach room D early by hugging the books behind it, though there's little to no point to doing this.

1 - Necklace of Protection VI - +55 PDef - Room A

2 - Bracelet of Perception VI - +55 MAtk - Room A (Must defeat Fire Monarch)

3 - Great Elemental Crystal - Room A (Must defeat Fire Monarch)

4 - Black Diamond - Room B

5 - Emerald - Room B

6 - Bracelet of Wisdom VI - +55 MDef - Room B (Must defeat Thunder Czar)

7 - Mythril Nugget - Room C (Must defeat Evil Shah)

8 - Earrings of Activation VI - +85 Inf - Room C (Must defeat Evil Shah)

Unfortunately, there's no healing circle or teleporter, so you'll have to leave and run through the whole dungeon again to restock, but once you're ready, step onto the rug and challenge the Demiurge NEO.
Recommended party: Alice, Sanae, Sakuya, and two of Marisa, Satori, Reisen, or Yuugi in Poison Shield formation (with Alice as decoy) and either Cirno, Mokou, Nitori, Patchouli, or Aya as commander.

The Demiurge NEO will act twice per turn and can use Strong Acid, Moulin Rouge, Holy Zapper, Inazuma Slash, Poison Hand, Dark Zapper, Special Missile, Drill, Headfirst Charge, Vortex, and its default Strike attack. Additionally, it'll always Concentrate on the first turn and then every three turns after that (1, 4, 7, 10,...). The turn after Concentrate, it'll always use either Rowing Flame, Frozen Coffin, Gibnut Zarnica, Zerstorung Felsen, Jesus Crush, or Zalam Iblis as its first action. On the defensive side of things, its 2999 regen on top of its titanic PDef and MDef AND its 200k health pool means there's no way around a long fight.

Alice should be equipped with the Yata no Kagami, Yasakani no Magatama, and Forcefield, and she should use Decoy on the first turn and Marionette Parar (or Rainbow Parar if it's off cooldown) every turn after that, except after Concentrate. If Alice is at level 70 and is equipped with the Hairpin of Swiftness V, she should have 257 Speed, exactly one point higher than the Demiurge NEO's 256 Speed and, thus, enough to outspeed its 999% speed spells with Little Legion. Sanae should focus on buffing the party, giving priority to PDef and MDef, and use Miracle Omikuji or Source of Rains to revive anyone who goes down. Sakuya should cast Colosseo World the moment the fight begins to stop its regen, then spam Soul Sculpture and Full Moon Revenge. The Demiurge NEO is too evasive for Elegant Killing Doll to be reliable, and Private Square will just override Colosseo World. Marisa should use Final Master Spark and Triple Spark whenever they're off cooldown and use Rapidfire Master Spark and Super Magic Napalm otherwise. Satori should use Dark Giga Flare whenever it's off cooldown and Flare every other turn. Reisen should use Hallucinogenic Tuning (prioritizing PAtk and MAtk before droping Eva, PDef, and MDef) and Stare of the Hazy Phantom Moon whenever they're off cooldown and Disorder Eye (if she has 20 points in Fascination) or Metaphysical Mind and Mind Explosion every other turn. Yuugi should equip the Galaxy (as it slays Elementals) and alternate between Knockout in Three Steps and Wind Blowing Down from Mt. Ooe. Once she runs out of Bombs, set Berserker Soul and use normal attacks.
Note: If you slip past the boss into room D, you can try to get Susanoh's Arm to drop from Susanoh, which can be used to synthesize the Ama no Murakumo no Tsurugi if you've already beaten Resentment Incident. You won't be able to ignore physical resists with it, but the high PAtk, all stats up, and 75% slayer effect on Elementals could make Youmu, Remilia, Nitori, or Mokou viable damage dealers in this fight.

For commanders, Cirno can reduce the odds of Bomb Reduction and Removal as either of those effects activating can be reason to reset entirely, though that's all she's good for. Mokou can revive party members and help Sanae focus more on keeping buffs up. Nitori will increase the damage from Marisa's and Satori's Mystic attacks while giving you an alternate way of avoiding the Demiurge NEO's spells. Patchouli can increase Marisa's and Satori's damage while also lessening the damage of the Demiurge NEO's spells. Aya can guarantee the party outspeeds the Demiurge NEO's spells, freeing up an accessory slot for Alice.

If you're struggling, ZeldaFan024 has informed me that the Demiurge NEO is susceptible to Silence, which can shut down much of its arsenal if you manage to land it. They said they managed it about 40% of the time, so it's doable if you build for Infliction.

No matter what you do, this will be a lengthy battle of attrition, but after a while, you should come out on top just fine.

Defeating the Demiurge NEO will earn you the achievement Great Emperor and increase the level cap from 70 up to 99.
Thankfully, all your EXP gained since reaching level 70 has been saved, but each party member will need to enter a fight and gain at least 1 more EXP point to properly apply it and update their levels.

Additionally, you'll properly gain access to room D (without needing to slip past), which has more powerful enemies than the rest of the dungeon and a single chest containing a Flower.

Finally, two more quests will open up.
"The Elemental Emperors Strike Back" will open the Library Depths back up and allow you to rematch the Demiurge NEO for more Great Elemental Crystals, and "Path to Power" will open up the Myouren Temple Depths for you to raise the Pow Limit.

As soon as you take Path to Power, the dungeon will appear over by the Myouren Temple.

Myouren Temple Depths is a blissfully short dungeon. It opens up with a four-way fork. One leads to a dead end room, two more loop back on each other, and only one reaches the back end of the dungeon to face the boss. Unlike Library Depths, there's nothing blocking your path, so as long as you know the correct door, you can walk straight to the boss.

Room A:

Room B (middle left path):

Room C (both right paths):

Room D (far left path):

Just pass through the middle left passageway...
And you'll find the boss through the door in the back of the hall.

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Fun fact!
Room D actually has two spots where you can get out of bounds.
These two walls have no collision, allowing you to explore two small out of bounds areas I've marked on the map. There's no reason to do this beyond the novelty of it, though.

1 - Earrings of Rebellion VI - +55 Res - Room D

2 - Diamond - Room D

3 - Goggles of Direct Hit VI - +85 Acc - Room D

4 - Goggles of Avoidance VI - +55 Eva - Room C

5 - Mythril Nugget - Room C

6 - Hairpin of Swiftness VI - +90 Spd - Room B

7 - Platinum Mimic(!?) - Room B
The Platinum Mimic will always ambush you, even ignoring Aya's ambush prevention, and attack 3 times per turn. I recommend running Poison Shield with Alice as a decoy, and give her as much physical resistance and PDef as possible to survive the ambush turn. Afterwards, use Illusionary Dominance or Shocking Photo to guarantee you outspeed, then wipe it out with your most powerful attacks.

8 - Necklace of Rage VI - +55 PAtk - Room B

9 - Black Diamond - Room B

10 - Relic of the Gods - Room A

11 - Flower - Room A

Just like in Library Depths, there's no healing circle or teleporter before the fight, but you can get here from the exit rather quickly. Once you're ready, step onto the mat to face off against the Archangel.
Recommended party: Alice, any four of Byakuren, Patchouli, Satori, Akyuu, Sakuya, Youmu, Mokou, or Yuugi. Formation can be Hakurei Barrier Formation/Hakurei Type, Moriya Destruction, Poison Shield, Attacking Defenders, Magician's Circle, or Hyper Library depending on who you choose to bring. Depending on formation, you may want Akyuu or Sanae as commander.

The Archangel will act three times per turn and can use Star Hand, Holy Zapper, Divine Gate, Holy Breath, various multi target debuffs, and its default Strike attack. If the land is pushed far enough towards Dark, it'll also start using Diabolic Breath. Additionally, it can use Concentrate, which it'll follow up with Punish the Judgment on the next turn. If Satori hasn't learned that from the Seraphim yet, it's technically easier to get here. Defensively, it's nowhere as tanky as the Demiurge NEO and only regens 2k in Light land, though it does have 50% Divine Shield, so make sure you bring weapons with enough Exorcism.

Your party should be well equipped with both Light and Dark resist to reduce the damage from the Archangel's barrage, and Alice should have Decoy active to draw attacks towards her. If possible, keep her alone in her column to minimize the threat of Holy Zapper. If you see Concentrate, Little Legion immediately. Byakuren should set Dark Sword on your physical attackers, then start applying buffs. Once the party is stacked up with P/MAtk and P/MDef buffs, swap to spamming Nirvana's Cloudy Way in Purple and then Dark Hole once she runs out of Bombs. If someone's low on HP, use either of Dark Heal or Light Heal (or the spell variants, if they're especially low) depending on your formation. If your formation makes it tricky for Byakuren to heal, Sanae's and Akyuu's commander spells can help supplement. Patchouli should have the Awakened Soul and spend the whole fight spamming Silent Selene. Satori should spam Zalam Iblis until she runs out of Bombs, then switch to Dark Flare. Akyuu should alternate between Bad Fortune and Dark Wall. Sakuya can set Private Square or Quick Time, then let loose with Elegant Killing Doll. When Private Square/Quick Time is on cooldown, use Full Moon Revenge instead. Youmu should set Human Realm stance and Fearless Before Danger, then alternate between Slash of the Eternal Future and Full Moon Slash. Mokou should alternate between Fujiyama Big Eruption and Final Finger (Soul Finger if she doesn't have Saint/God/Phoenix Hand equipped). Yuugi should alternate between Knockout in Three Steps and Wind Blowing Down from Mt. Ooe, then set Berserker Soul and use physical attacks after running out of Bombs.
Note: If you've synthesized the Ama no Murakumo no Tsurugi, its 100% Exorcism, high PAtk, 75% Deity slayer, and various stats up make it a wonderful choice to give to any of your physical attackers.

Like with Demiurge NEO, this fight will be rather lengthy no matter what, but overall, it's not quite as hard. If you can get here, you can absolutely take it down.

Defeating the Archangel will award you the Archangel Killer achievement and increase the Pow Limit for all characters from 99 to 125.
I assume it works the same as with the level cap, storing any Pow earned until the Archangel is dead, then awarding it all at once as soon as you earn a single bit of Pow EXP, but I can't be too sure as all my party members were sitting around 80 Pow around this point. Unless you do some serious grinding (and I already did hours upon hours upon hours of material grinding, plus some level grinding to reach level 70), you're not even gonna be close to 99 Pow when you do this, so it's not a worry regardless.

Additionally, you'll unlock a new quest.
Taking "Divine Punishment!" will reopen Myouren Temple Depths and allow you to rematch the Archangel for some Relics of the Gods.

With the exception of the Towers, all new youkai in these two dungeons are considered to be found in Incident Level 5, and the vast majority of them are shared across both.

Highway Star - A stronger version of the Impellitteri found in the Dark Space. Their normal attacks hit everyone for incredible damage, and their bulk is nothing to scoff at. They're often worth a Private Square on their own, and running into more than one is reason the run the other way.
Found in - Library A, B, C, D ; Temple D

Harpyria Empress - A stronger variant of the Harpyrias first found in Forest of Magic 2. They can inflict party wide Confusion and will often multiply if left alone.
Found in - Library A, B, C, D ; Temple D

Spa Ciara - A dragon with a preference for Fire attacks and Charm. Not too dangerous overall. It has a 10% chance of dropping the Ryuujin Shield.
Found in - Library A, B, C ; Temple A, B, C, D

Silver Mining Village - A stronger variant of the Mining Villages found in Hieda Manor Basement. They're just as annoying with their tendency to use Imposing Stance, and they can use Sacrifice Bomb if left at low HP. It has a 10% chance to drop the Muscle Belt V, which gives +200 Max HP.
Found in - Library B, C, D ; Temple A, B, C, D

Ogre King - A stronger variant of the Ogre found in Hieda Manor Basement. It's an incredibly bulky and powerful physical attacker. It'll often use Gather Strength and follow up with either Headfirst Charge or Total Destruction, which will likely either party wipe you or just annihilate Alice if you used Little Legion. It has a 10% chance of dropping Shuten Douji's Wrists, an improved version of Shuten Douji's Wrist.
Found in - Library - B, C, D ; Temple - D

Queen Basilisk - Yet another tier of Basilisk. Not too dangerous overall. It can use PSN Breath and DTH Breath, but its weakness to Light should get rid of it pretty quickly.
Found in - Library B, C, D ; Temple B, C, D

Succubus Queen - A stronger version of the Succubus found in the Garden of the Sun. The only real threat it poses is party wide Charm. It's otherwise easy to deal with.
Found in - Library A, B, C, D ; Temple D

Death Realm Petals - A stronger version of the Qliphoth Petals found in the Lakebed Temple. They can still inflict party wide Sleep and Death.
Found in - Library A, B, C, D ; Temple D

Will Galgalim - A stronger variant of the Galgalim found in the Lakebed Temple but with access to Mental Blast and defense buffs now. It's incredibly bulky and often worth just running from.
Found in - Library B, C, D ; Temple D

Sophia Cherubim - A stronger version of the Cherubim found in the Gorgon Sanctuary but with access to attack buffs now. It's even bulkier than the Galgalim, though it has a 15% chance to drop the Magic Ring V, which gives +100 Max MP.
Found in - Library C, D ; Temple D

Death Revenger - A stronger tier of the Death Rider from the Gorgon Sanctuary. Its Drain Sword is strong enough to even chunk Alice. It has a 10% chance to drop the Aufheben.
Found in - Library D ; Temple C, D

Gelatinous Matter Emperor - Yet another slime enemy. It's bulky enough to survive a couple turns, and its Thorough Digest is threatening even to Alice.
Found in - Library D ; Temple A, B, C, D

Enraged Qilin - An incredibly dangerous enemy with access to Mental Blast, Leaf Barrier, DTH Breath, and various other Mystic attacks. It's the first enemy available that can drop Akyuu's gold material, though.
Found in - Library D ; Temple, B, D

Denki Bran - A Thunder variant of the mages found in Grand Temple, Dark Space, and Hieda Manor Basement. It's largely non-threatening as long as you don't let it build Thunder land.
Found in - Library D ; Temple A, B, C, D

Vacant - A stronger version of the Voids found in Lakebed Temple. Simple to kill, though they can use Meteor and Annihilation.
Found in - Library D ; Temple A, B, C

Lastbeard - A stronger version of the Backbeards found in Lakebed Temple. It still reflects physical attacks, can inflict Silence, and has access to Thousand Needles.
Found in - Library D ; Temple A, B, C, D

Tower of Hell - A bulky enemy with access to Imposing Stance and a tendency to set Fire land. They often spawn with Spa Ciaras.
Found in - Library A ; Temple B

Tower of Gaia - A bulky enemy with access to Imposing Stance and a tendency to set Earth land.
They often spawn with Death Realm Petals.
Found in - Library A, B

Tower of Babel - A bulky enemy with access to Imposing Stance and a tendency to set Thunder land. They often spawn with Denki Brans.
Note: Due to an oversight, Gaia and Babel had their shields swapped. The compendium info reflects this, but keep it in mind.
Found in - Library D ; Temple A, C

Susanoh - A powerful midboss tier enemy with Slash and Light attacks. It spawns alone or with a Silver Mining Village in the Temple, and it spawns alongside Uzubogikhi in the Library. It has a 20% chance to drop the Catastrophe Blade, an improved version of the Disaster Blade dropped by Hina.
Found in - Library D ; Temple C

Uzubogikhi - A weaker variant of the Uzubogikhi quest boss likely already fought in the quest Magic is Forbidden Here! However, unlike her quest boss counterpart, she has access to Comet, Meteor, and Mystic skills. She spawns alone in room C of the library and with Susanoh in room D, and she has a 20% chance of dropping the Wizard's Wand.
Found in - Library C, D

Rune Elemental - A nearly midboss tier enemy that often spawns alongside Vacants in the temple. It's resistant to all magic, immune to Mystic and Void(!?), and weak to all physical elements, though it attacks twice per turn with powerful Mystic attacks. It has a 15% chance to drop the Hyper Orichalcum Knife.
Found in - Temple B, D
Fun fact! The Rune Elemental was designed by one of four winners of one of two official Touhou Card Monsters tournaments.

Yukkuri Sisters x6 - This can be found rarely in room A of both dungeons, though it's not much notable at this point.

Yukkuri Emperor, Yuckuri x1-6 - This can be found rarely in room B of both dungeons and is a consistent spot to find Yuckuri.

Yukkuri Emperor, Yuckuri King, Yuckuri Sisters x1-6 - This can be found rarely in room C of both dungeons and is a consistent spot to find both Yuckuri Kings and Yuckuri Sisters.

Yukkuri Emperor, Reimu Emperor, Stray Yuckuri x1-6 - This can be found rarely in room D of both dungeons and is a consistent spot to find both Reimu Emperors and Stray Yuckuri.