You're Not My Boss! Achievement in Doom 3: BFG Edition
You're Not My Boss!15
Defeat Sabaoth boss in DOOM 3
How to unlock You're Not My Boss!
Story related and cannot be missed unless he commits suicide by blasting himself against one of the pillars with his own BFG.
This boss is Sergeant Kelly, but he has become mutated and possessed. A really easy and quick way to kill him is to make sure your Soul Cube is charged before entering the room for the fight and then right when the boss says the word “welcome,” launch the Soul Cube and then fire FIVE rockets and he should die in a few seconds.
Here is a speed kill video by xirvin92:DOOM 3 KILL SERGEAT KELLY IN 5 SECONDS - YouTube