Nioth-Korghai

Nioth-Korghai appear octopus-like, but are in fact a dark-orange, "bundle of fungoid creepers joined together at one end"—so essentially tentacles without a body.

In the RPG...

Nioth-Korghai have numerous special abilities. First of all, with an opposed POW roll, they can possess the body of a human, who will have blackouts when the Nioth-Korghai feeds. At its base POW, this has a 67% chance of working against an average human—and its POW only goes up as it feeds. A fully-fed Nioth-Korghai has an 85% chance!

    Next, they can also alter their own body shape to mimic another lifeform, or even inanimate object, but it costs them an average of 27 POW to do so. I'm curious how this works with regard to size. As in, how does a 140 SIZ Nioth-Korghai shrink down to a 65 SIZ human? Presumably they would retain their mass, so perhaps this could be used to detect their mimicry. 

    Another ability is to create an psychic energy blast thats strength is determined by how much POW is put into it. Expending all of its POW, a fully fed Nioth-Korghai could create a blast averaging 77 damage! 

    Nioth-Korghai are also vampiric, able to drain the life force of intelligent beings. This attack drains an average of 16 POW, as well as 9 CON and 9 APP, all of which cannot be regained. The stolen POW goes directly to the creature's POW (up to double its base POW). An odd side-note: if a victim is drained slowly, a Hard INT or POW roll will psychically link the victim to the Nioth-Korghai. 

    One last ability—though more like side-effect—is that someone fully drained of POW becomes infected. After two hours, the dead, dried husk of a corpse awakens, driven to feed on others' life forces. Once fed, they regain all lost stats except for INT as well losing all Sanity. This feeding must occur every two hours or else they die... again. Each victim then becomes infected themselves, continuing the cycle. Killing the original Nioth-Korghai will stop the plague, and all infected die instantly.

    Every stat except DEX has changed in the 7e Malleus Monstrorum, though the averages for STR, CON, and SIZ remain the same. INT has been increased and POW has been decreased.

In a video game...

Based on the ability to infect people, the Nioth-Korghai would probably work in a video game just fine. The player would have to fight their way through the infected to kill the source and stop the spread. The only caveat to its inclusion would be the crazy-powerful energy blast. It would obviously need to be limited in some way.

In a film...

I'd never actually heard of the Nioth-Korghai before writing this, but I think they would actually work quite well in a film. Zombie/Vampire films are a dime-a-dozen, but with the inclusion of a tentacled alien at the source of the virus, it could just be unique enough to stand out from the crowd.