DOOM: Eternal: How to beat the Marauder
DOOM: Eternal can be a challenging game, and the Marauder boss (your first encounter with this sort of enemy) represents both a critical story moment and one of the absolute toughest parts of the campaign. Many of the weapons, tactics, and techniques that you've learned up to this point in the game don't serve you well in this fight, due to the Marauder's defensive abilities and the extremely compact arena in which the battle takes place. Beating the Marauder takes a mastery of dodging and rapid reflexes, as well as patience - because you're likely to die a lot in the process.
If you're having trouble killing the Marauder boss, here are some tips.
#1: Keep to the middle distance
As outlined via the in-game tip text (seen above) the Marauder is ready to punish you if you get too close or too far away. This is probably the biggest difference between this fight and the other challenging ones up to this point in the game, because in DOOM: Eternal's brutal arena fights against dozens of foes, you get used to dodging away and dashing into the distance when things get too intense, so you can go farming lesser demons to replenish health and ammo.
In this fight, that's much more challenging. You need to stay close - in Super Shotgun range, really - to have the best chance of hitting the Marauder when he's vulnerable and to avoid his extremely damaging long-range attacks. To succeed in this fight, you have to focus on staying close, which goes against the requirements of most of the game up until this point.
#2: Watch and listen for the moment to strike - and use the Super Shotgun
The game tells you when to hit the Marauder: when his eyes flash green. The best weapon for this is likely to be your Super Shotgun, since the high damage and spread means that you'll make the most out of every hit, and you aren't likely to miss if you're in close enough.
The Marauder does a lot of dodging, but when he's about to open himself up for a hit, you'll see the green flash and you'll hear a specific sound effect. Train yourself to fire right at that moment, every single time.
#3: Upgrade the Super Shotgun, and replenish its ammo when it runs out
If you have weapon points to spend, you'll want to make sure you have the "Fast Hands" upgrade on the Super Shotgun. This speeds up reloading time, and that allows you to potentially get off two shots before the Marauder recovers, if you strike at the right moment.
When you run out of ammo with the Super Shotgun, you're in a pretty bad shape. None of the other weapons in your arsenal are really up to the task of doing massive damage in the split-second timing window. If you're scrambling for a backup, the Chaingun does alright - but your best bet is to go running for the nearest lesser demon the moment you're out of shotgun ammo, and chainsaw through them to refill your clip.
#4: Use your flamethrower often
You need to do everything possible to keep your health and armor up in this fight, because you'll be taking a lot of damage. One great way to do this is to spam your flamethrower regularly, to keep both the Marauder and the other enemies in the room aflame and shedding armor pickups. Since the space is so confined, you'll pick all of these up just by moving around during the fight, and that can make the difference between living and dying in this brief, intense battle.
#5: Kill the dog, ignore the others (except for health farming)
The Marauder repeatedly summons a flaming dog spirit to attack you, and it can be brutal. It's fast, its attack distorts your vision, and it intelligently flanks you. A few seconds spend trapped between the hound and the Marauder are enough to end the fight - so don't let things get to that point. As soon as the hound spawns, kill it. You can switch weapons if you have the presence of mind to do so, because you don't need to waste shotgun ammo on the dog, but things will probably be moving too fast for you to have that breathing room, most of the time.
Don't bother aiming your weapons at the other demons that spawn in the room, except as needed to stagger them for glory kill health. You're going to be dodging so much as it is, their attacks won't be doing much damage, and they'll continually respawn regardless of what you do. The only time you pay them any specific attention should be when you're farming them for health or ammo.
#6: When the Marauder dashes, you should dash too
One of the Marauder's most punishing moves is a quick double dash that brings him alongside you, followed by an axe swing. He'll do this a lot if you let him, so you should get used to matching him, dash for dash. He wants to close in and move to one of your sides, so you should dash away to preserve the right amount of distance, and turn to keep him in your view.
Follow these tips, and you'll win the fight - eventually. Don't get frustrated if it takes you a few tries - just keep that Super Shotgun ready, and wait for the flashing green to strike.
Important note: This guide is focused on your first encounter with the Marauder enemy. Subsequent battles will require adjusting your strategies, but there's one more universal tip: don't waste BFG ammo on the Marauders. They'll block your super-weapon with their shield, and you'll be very sad.