DOOM 3: BFG Edition

Once you defeat the second boss and tag achievement 'Gimme Power', you will unlock the Artifact's Berserk ability. This ability is only applied to the player's Fists. In order to tag this achievement, use 'LB'/'RB' to select the Artifact, press 'RT' to activate Hell Time, 'Back' to go to your PDA, 'LB'/'RB' across to Inventory and 'X' to equip your fists. You are now prepared to make minced meat of pretty much any enemy you find.

Find yourself a cluster of 3-5 enemies. Run into a room where you can activate the Artifact and equip your fists. Then, run back into the room and mulch your enemies. With luck, more enemies will spawn in after you're done cleaning up the first lot, leaving you to mop them up with what little Hell Time you have remaining. Do this a couple of times and you'll tag this achievement.

EDIT: You can press Right on the D-Pad to switch to your fists. Props to tibor b for telling me, apparently my D-Pad is defective. >_>

What I done was that as soon as I got the berserk for the Artifact, I went to Phobos station 1 and when you go into the room where there is the window looking out onto Mars, I saved and activated the berserk ability and I killed the guy who comes running around the corner, the two marines around the corner by the health station and the workers just through the door. sometimes the most kills I got was 6-7 but you just load up the save and do it again until you get the achievement. This can only be done with the fist which you can equip through the PDA or just press the right on the d-pad.

EDIT: it took me about 4 reloads to get the achievement.