Dream master antag:
Basically kind of a two person team antag although they don't have direct contact or communication with each other. Basically one player takes on the incorporeal part, an entity that haunts the station. At the start of the round it picks a spot to hide its remains (has to be somewhere on the station z-level and it can't be on a space tile). It can't attack people directly. Instead, it lulls them into a deep sleep and drags them into a dream world.
This is where the second player comes in. They appear as a husked corpse in this world wielding a bladed glove. When someone's pulled in he gets a message informing him as such and that's his cue to start hunting. You don't want to fuck with this guy if you get dragged in. His powers are kind of limited at first but he's still extremely dangerous.
First of all, he's invincible. You can knock him out for a moment but even if you keep wailing on him he'll jump up after several seconds with an ear shattering roar that stuns anyone near by. He's got aforementioned bladed glove which does a shit ton of damage and can't be disarmed. He can jump into objects to sort of jaunt around to some degree or lay in ambush for his victims. He can also send messages to the people in the dream world in different ways such as Centcomm announcement, whispers in their heads, radio or regular messages from other people, etc. (Since this is the shitty suggestion thread, maybe admin PMs (Admin PM from Jason Esword Gloves "Hi, mind explaining what went on with that assistant and why you are FUCKED NOW, BITCH")) to taunt them or mislead them. As he kills people, he steals their souls, unlocking new powers such as being able to set floor traps that slow or stick people in place, increases the damage his glove does, and a bunch of other shit.
Getting sucked into the dream world isn't an instant game over, no rez however, although you'll need some quick thinking and fancy footwork to survive. Like I said, the dream master is invincible but he still has to hunt you down so your only options are to run, hide, or find ways to sneak by him (might be even more efficient if LoS makes it in although hiding in the shadows works), or temporarily incapacitate him. Normally you'll stay asleep for 15 minutes but if someone injects you with epinephrine you'll wake up much quicker.
The only way to truly kill the dream master is to destroy its physical body via incinerator, super matter shard, etc. or alternatively have the chaplain douse them in holy water. If the dream master steals x amount of souls, they win. If the crew destroys the remains however, anyone currently trapped in the dream world will awaken and both of the dream masters will die.
I watched a marathon of Nightmare on Elm Street on IFC today.