First phase is a normal AC fight, but he's accompanied by ~5 weaker ACs that are constantly getting in your crosshair messing with the aim. What's worse is they all look almost the same so you have to glue to the boss.
Second phase is him in a new, stronger AC and 2 c-spiders in second phase against you and another AC, which does nothing useful.
After you kick him to half hp, the third phase starts - he kills off all bystanders and starts getting in your face with 3+ hit sword combos.
Do I need to mention that you get zero resupplies? I've been running the usual dual chainguns, and half of the time I've been left with no ammo by the end of it.
Fuck, on my successful attempt I also lost chaingun ammo, and finished the fight by stunning him with spikes and doing a boost kick