DOOM II (Classic)

MAP 16 is your best bet for this level. You should have the BFG from the previous level, follow from the beginning of the level to the blue key. Once the blue key is picked up hordes of imps are spawned. Fire away! Check out the video below for guidance.

Map: Tricks & Traps (Level 8)
Difficulty: Doesn’t matter
This guarantees an early BFG. Can be done solo or on Multiplayer.

The first room you’ll need to enter has two rotating pillars at the end. There’s a Plasma Gun behind the pillar on the right and a button to push on the back wall to the left (that will help in the next room.) Cacodemons come to stop your attempt to exit after you get to the back. If played on Ultra Violence, there will be a Sergeant on the steps down. Shooting him attracts the Cacodemons. Dispatch them however you like.

The room next door (green walled) is where the BFG will be. Pinkys descend to say hi after you nab the Rocket Launcher and ammo for it (or if you already have the Launcher from a prior level, walk to that location.) Welcome them with weaponry and push both buttons they guarded. This further opens another section (where the Rocket Launcher sat.) More Pinkys ambush you upon collecting the Life Orb. Clean house and punch the Demon Wall to reveal the BFG. Grab the ammo backpacks on your way out for good measure.

Enter the room with the Imps a floor below. They will all be facing away from you so they won’t be alarmed upon entry. Forgo the shotgun if you want and fire the BFG. Most (if not all) of the Imps will die and the achievement pops shortly after. This room is helpful if you are going for the Super Shotgun achievement as well.