Axilus Prime

The one at night, Fishy. I found that one harder than anything before it, harder even than the two Wardens fight (which hilariously enough I found fairly easy)

I found a way to cheese that Warden battle. There's a Carbine and an unlimited ammo crate up high and very far away from him. With enough patience, you can shoot him in the face until he dies.

I used that crate, but the position's actually vulnerable to Incineration bombardment and to his black hole attack. Plus I'm not quite that patient. I found a quick and easy enough method after some trial and error though. Run up the right, grab the Incineration Cannon If you have a Carbine, use it, if not, get from that place then run back. Kill both Watchers, then actually kill both Knights. You MUST get them during that brief moment of headshot vulnerability.