I was inspired by Niksar's post The Twins.
Main Concept:
A large amalgamation of corpses of past interns fused together by something that is clearly not a good surgeon due to the excessive amount of limbs. Once it has grabbed someone the only way out is to zap gun it while killing it could cause it to split making it either slower or faster.
Behavior:
Normally it sits on the ground or slowly walks around to find a new place to sit and look at lights since it has swelling around the eyes making it hard for them to see players so it will observe bright areas while it remains in the dark. As it has multiple bodies controlling it they might attack their other heads which would be the only sounds they make when sitting. It sits up slowly and screeches when it spots a player but, due to its size, it will stumble and get stuck occasionally, especially in doorways, in which case it will move back and try to find a new spot to ambush again. In hallways, it will use its arms to pull it along the walls making it significantly faster this way players would get used to a monster in a weaker state so they can be surprised by a much harder monster in facility dungeons although it if only spawned on high ends this would hurt Titan too much.
Absorption Ability:
Similar to the masked enemies the amalgamation will absorb corpses increasing its overall size and damage while it moves only slightly slower. It's aggression towards both players and itself can also increase with more interns. I also thought the beast could block hallways but I'm pretty sure this could be disruptive to the gameplay loop. Maybe a stumbling mechanic could allow players to climb on top and over the monster.
Drops:
He had the idea of multiple masked enemies fused together that drop a valuable heart but I couldn't think of anything specific for my idea to drop so I thought it could drop one piece of equipment, like a shovel or radar booster, and one scrap when killed or when it stumbles.
