This is my guide for how to fight certain enemies in Doom Eternal.

Doom Eternal is a fun game that goes alternates between hectic arena style fights and almost enemy-less exploration. The maps are pretty linear but it does have a lot of side nooks and cranies stuffed with power ups, armor, ammo, extra lives, and secrets.

Basic tips are:
* The enemies will swarm you and try to stop you from moving.
* The AI is very basic, and it will trap you and kill you.
* Moving around and dashing from time to time is the only thing keeping you alive.

My favored weapons are:
* Combat Shotgun with Sticky Bombs (mastered)
* Heavy Cannon with Micro Missiles (mastered)
[The scope mod is useful in the beginning but after that is virtually ignored]
* The Plasma Gun and the Heat Blast mode is very useful against shield enemies
* Super Shotgun with Meat Hook (mastered)
* Ballista in Arbalest mode (mastered)
* BFG for Arch-Vile encounters only

My favored runes are:
* Seek and Destroy - launch into glory kills from further away
* Equipment Fiend - enemies killed by equipment lowers recharge time
* Punch and Reave - enemies killed by blood punch drop health

This is my preferred order of Praetor Suit Tokens:

3: Exploration: Item Finder - reveals the position of all progression items on the automap.
2: Environment: Thicker Skin - immune to damage from barrel explosions.
2: Environment: Explosive Pinatas - barrels will leave behind some ammo when destroyed.
2: Environment: Regenerating Barrels - barrels that have exploded will respawn once after a short duration.
4: Fundamentals: Hit and Run - dash refilled on glory kills.
2: Fundamentals: Hot Swapper - faster weapon switch and mod swap.
1: Environment: Hazard Protection - RAD suit takes less damage from toxic sludge and toxic water.
** Note: you should have Hazard Protection before entering the Super Gore Nest level.
4: Fundamentals: Faster Dasher - dash refills more quickly.
2: Exploration: Bigger Fog Lights - larger automap reveal radius.
1: Exploration: Item Classifier - reveals all progression items on the dossier.
1: Fundamentals: Grappler - faster ledge grab and monkey bars.
1: Exploration: Slayer Atlas - reveals the automap station location on the automap.
5: Ice Bomb: Frost Bite - damage dealt against a frozen demon is increased.
4: Ice Bomb: Ice Drops - damaging and killing frozen enemies will drop health.
3: Ice Bomb: Permafrost - demons remain frozen for longer.
3: Ice Bomb: Faster Ice Cooldown - takes less time to cooldown after firing.
5: Frag Grenade: Frag Stock Up - fire twice before requiring a recharge.
4: Frag Grenade: Scatter Bombs - each demon killed by the grenade explostion spawns scatter bombs.
3: Frag Grenade: Faster Frag Cooldown - takes less time to cooldown after firing.
3: Frag Grenade: Combustion Concussion - the grenade emits a second, larger, non-damaging explosion that falters demons.
END
TOTAL: 55 Points

SECRET ENCOUNTERS
Secret Encounters give you weapon points for weapon upgrades. I usually avoid them the first time through a level, and then replay the level with various cheats on. More really to practice and to take the pressure off of the Secret Encounters. You can play Secret Encounters with cheats on. Most Secret Encounters are easy enough to just spam rockets and you're golden. However, there are two Secret Encounters that require precision. 1) the Marauder Secret Encounter in Taras Nabad, and 2) the Doom Hunter Secret Encounter also in Taras Nabad.

SLAYER GATES
Slayer Gates give you an Empyrean Key. 6 of these keys will unlock the Unmakyr. The Unmakyr is a fun weapon but doesn't really surpass the usefulness of the BFG in my opinion. It's fun to get just for the sake of completing everything. You can NOT play Slayer Gates with cheats on (the Slayer Gate Key will not show up in the map).

1-UP MODE
This plays through the campaign mode but you can NOT use the Mission Select to replay missions. Which effectively means you get 1 chance to play Slayer Gates and 1 chance to get each Secret Encounter. You do not have to get the Secret Encounters or Slayer Gates to complete the game or 1-Up Mode. You must complete 1-Up Mode on any difficulty with 10+ extra lives remaining in order to get an achievement.

Doom Hunters are actually fairly easy to fight, they're basically a mini-boss that has guns, rockets, and a chainsaw.

First Stage
The first stage of the Doom Hunter he's on a platform and can hit you ranged and melee with bolts, missiles, and chainsaw. He has a shield that reduces the damage he takes but it can be temporarily disabled with the plasma gun. When his shield is down he takes more damage in the head it seems. Once his first lifebar is depleted the platform will be destroyed and fall off.
Preferred Weapon: Plasma Gun

During the platform falling off he says "Critical Damage!" and seems to be temporarily invulnerable.

Second Stage
The second stage of the Doom Hunter has him as a flying torso. He has a ranged bolt and the chainsaw. He seems to have less health in this form and is overall less dangerous at this point.
Preferred Weapon: Bottomless Missiles

When you're first introduced to the marauder, you fight him alone. After that he starts showing up with more and more ally enemies.

Basic formula for fighting him is:
* Keep some distance between you two.
* Kill his companion enemies first and foremost, avoiding him as much as possible.
* When he summons his hound, kill it first.
* When his eyes flash green you can do the Super Shotgun/Ballista combo but I just prefer to shoot him twice with the Super Shotgun from point blank--backing off after that 2nd hit.
* Your time to attack him after his eyes flash green is extremely limited--if you're not fast enough you won't get two shots in, just one. I didn't see a large difference between the number of hits required with the Super Shotgun and Ballista to really matter so sticking with the Super Shotgun for me was just easier.
* Chainsaw a nearby zombie to get fresh ammo if needed.

** Sometimes you can land a frag grenade behind him where it will damage him regardless if he has his shield up or not.

One-on-one this guy is pretty easy to take on, it's the later parts where he shows up with others that makes him the most difficult. Especially Whiplashes (the snakes) and the Carcasses (the shield producing enemies).

The Khan Makyr is a battle that takes place on a floating island style arena--she flies around the arena with her servants constantly taking pot-shots at you.

For this arena you'll need to remember to constantly keep moving--staying off the damaging floor areas while battling her.

You will need:
* The Combat Shotgun with Sticky Bombs mod with Five Spot Mastery
* The Heavy Cannon with Micro Missiles mod with Bottomless Missiles Mastery
* The Super Shotgun with the Flaming Hook Mastery

You will fight:
* red Makyr Drones
* the Khan Makyr

The basic strategy is this:
Alternate between attacking the Khan Makyr, and then after she gets a health bar knocked down, harvest the Makyr Drones, and then proceed to attacking her again.

ATTACKING THE KHAN MAKYR
* Switch to the Heavy Cannon.
* Spam the utter sh** out of the Khan Makyr's chest area with the the Bottomless Missiles
* When she's stunned use the Super Shotgun hook to zip up to her and punch her chest
* You may have to dash to her to get to a clear line of sight or get close enough to hook her.
* ALTERNATIVELY: Use the Ballista to attack her center chest area.

HARVEST THE MAKYR DRONES FOR AMMO
* Switch to the Combat Shotgun.
* Use the Sticky Bombs to score a hit on the Makyr Drones heads.
* You can use the Freeze Bomb here to make sure they don't move
* Once the bomb explodes it will drop a ton of health and ammo.
* Once should be enough but damage looking for them might mean you have to get a second one.
* Once you have more health and ammo switch back to the Heavy Cannon and repeat the process.
* ALTERNATIVELY: Use the Ballista to headshot a Makyr Drone.

This is a two stage boss:

FIRST ARENA:
You need to knock off the 8 pieces of armor to the Icon's body.
* Crucible ammo regenerates after a short amount of time.
* Blood Punch recharges regenerate after a short amount of time.
* As far as I can tell, the other ammo does NOT regenerate, including the BFG ammo.
* Random monsters constantly spawn in the arena while the Icon is attacking you.

SECOND ARENA:
You need to damage the 8 pieces of the Icon's body that was once armored.
* Crucible ammo regenerates after a short amount of time.
* Blood Punch recharges regenerate after a short amount of time.
* As far as I can tell, the other ammo does NOT regenerate, including the BFG ammo.
* Random monsters constantly spawn in the arena while the Icon is attacking you.
* There is a Supercharge Orb in the center of the arena, hovering mid-air--it does not respawn.

DON'T FORGET TO ...
* Grab the Ballista before going to the Super Gore Nest.

REMINDERS ...
* The cheat codes in the Doom Fortress are:
* Unlocked with batteries: ALL RUNES
* Unlocked near the end of the game: FULLY UPGRADED SUIT

CHEAT CODES:
1: Hell On Earth
Infinite Extra Lives *
There are 4 extra lives

2: Exultia
No Cheats
There are 7 extra lives - this has the most lives of any other level and it's only slightly longer than Hell On Earth (the first level).

3: Cultist Base
IDDQD - you're not invincible, but you take far less damage **
There are 6 extra lives

4: Doom Hunter Base
Silver Bullet Mode - kills a staggered demon in one hit
BOSS: DOOM HUNTER
There are 3 extra lives

5: Super Gore Nest
Infinite Ammo **
There are 4 extra lives

6: ARC Complex
IDKFA - all weapons mastered, all equipment fully upgraded
BOSS: MARAUDER
There are 3 extra lives

7: Mars Core
Onslaught Mode - damage is multiplied x4 **
There are 6 extra lives

8: Sentinel Prime:
No Cheats
BOSS: GLADIATOR
There are 2 extra lives

9: Taras Nabad
Overdrive Cheat Code - faster attack and infinite ammo **
There are 3 extra lives

10: Nekravol
Famine Mode Cheat Code - monsters don't drop loot ***
There are 3 extra lives

11: Nekravol - Part II
Party Mode Cheat Code - demons explode into confetti
Instant Stagger Cheat Code - any hit staggers demons, but not bosses
There are 3 extra lives

12: Urdak
Beserk Cheat Code - instant kill demons with your hands--RIP AND TEAR
BOSS: KHAN MAKYR
There are 3 extra lives

13: Final Sin
No Cheats
BOSS: THE ICON OF SIN
There are 4 extra lives

* this is a decent cheat for going back through levels and looking for gear, secrets, or challenges
** the best codes for going back through levels looking for gear, secrets, or challenges
*** this provides you with an achievement when using ONLY this cheat code