Here are a few of mine: (using My Hiro Hamada Doom WIP Mod)
1 - So I am confronted by a Macra (Spider Mastermind). The Macra is a huge crab, Ok? so the Macra follows me, and i just stood in SHOCK then laughed at what he did: The Freakin Macra Follows me, and SUCCESSFULLY follows me through that TINY HALLWAY in the background.
SCREENSHOT:

2 - My little bro is playing my mod, He fires the rocket launcher trying to hit a Dalek (Imp) and misses and hits the wall directly underneath the dalek. what happened to the dalek when the rocket had mpact with the wall had me laughing for 5 minutes: the dalek HOPS IN THE AIR.
3 - I shoot down a dalek on the high up on a building from afar in the original Doom II map, Downtown. when the dalek died, his corpse JUMPED OFF THE EDGE AND FELL ALL THE WAY DOWN TO THE GROUND.
4 - on the same level, earlier, I killed a dalek (Imp) in a window. I have it to where one of his deaths involves a custommissle, which is his head, fly off of his body and land somewhere. His head flys STRAIGHT OUT OF THE WINDOW.
5 - So, I have the Infernal Spider in as
Spoiler:. I made it to where
Spoiler:So, theres monsters EVERYWHERE. He spawns for the first timee, and I'm thinking: Oooh! He's here! if he gets into infighting, he will obliterate all of the other monsters, and... Oh, He'll kill me as well.
He dies THIRTY SECONDS AFTER HE SPAWNS.