Hi, new member here. I've had this idea for quite a while.

Inspired by the 1987 movie The Hidden, this creature requires hosts to live. It's intentions and alignment are a complete mystery. Design-wise, it would resemble Hidden's creature. It can squeeze through the tiniest of openings, which allows it to take even cyborgs as hosts.

Gameplay

When you select it, or win as it, the announcer does not say anything, adding to the mystery. It is currently inhabiting some unknown person, who's appearance will be completely random (the host could even be a character who didn't make it into the game). While in this body, the creature can only use it's own special moves.

An important part of the parasite's gameplay is body snatching. It's first host is dying, and if it doesn't switch bodies, it will eventually die. It would have a special finishing move allowing it to do just that.

Upon switching hosts, you can keep your current one for a maximum of three fights, but you are free to switch hosts anytime. When inhabiting in a host, you will get all his/her attacks, including the special ones, along with the creature's. It does not inherit the host's personality though, so no taunts when inhabiting Shao Kahn, but the creature does have some of it's own.

It would have it's own fatalities (as well as friendships, babalities, and the like.) and the body snatching finisher. Maybe it could even use it's host's finishers, some of them tweaked a bit.

Part 2 coming up.