Elden Ring is home to quite a few bosses that require a lot of planning and strategy, but Commander O'Neil is one of the most straightforward. However, that doesn't necessarily make the fight easy. This optional foe is more than capable of making quick work of you if you come at him at a low level.
As taking Commander O'Neil down is part of Millicent's questline, you'll want to know how to put him down so that you can reap the long-term rewards of following this important side-journey. Here's where to find Commander O'Neil and how to beat him.
Just reaching O'Neil is half the battle. You'll likely first approach the swamp from its west side, far from the Heart of Aeonia. Don't ride straight through the swamp to the site of the boss fight. You'll end up being invaded by Millicent, who will likely knock you into the swamp itself, and kill you soon after. Instead, circle around the swamp's north side and look for the Sellia Under Stair site of grace. From there, you'll be able to travel southwest to the site of grace just north of the Heart of Aeonia, called Inner Aeonia.
You'll find Commander O'Neil in the Heart of Aeonia.From here, travel southwest, around the Heart of Aeonia. You'll eventually find a small patch of land with a Stake of Marika and a summoning pool effigy. This is where you'll want to run into the boss fight from, as you can easily summon other players (although it's not the best choice) and run straight back in if you die.
Be sure to take these enemies out quickly though, because O'Neil can buff them. He can raise both their attack and defense, making it entirely possible for you to get caught up in killing them and ending up in the dirt yourself.
As soon as O'Neil's soldiers are down, target the big man himself. His attacks have a decent amount of reach but are easily avoidable as long as you don't get greedy. Hit and run tactics are best if you're using a melee build against the boss. If you're a ranged or magic user, on the other hand, you can simply keep your distance and chip away at his health with no issue.
There are only two attacks everyone should watch out for when fighting Commander O'Neil. The first has him spin his weapon in large circles, causing circles of wind to whip around. He spins his weapon a few times before a larger circle of Scarlet Rot envelops the area, instantly infecting anyone inside. If you end up getting hit by this attack, it's almost a guaranteed death. As soon as you see him preparing this attack, simply run away and you'll be safe.
O'Neil's other attack is activated once he's at 40% of his maximum health. He'll summon three headless axemen, all of whom can also be buffed similarly to his initial group of soldiers. Just like that other group, take out the axemen as quickly as possible, and get back to focusing on O'Neil with hit and run tactics. After defeating the axemen, O'Neil shouldn't be a problem to take out.
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