Ny’ghan Grii

Ny’ghan Grii are spherical, luminous beings with a single, faceted eye, and puckered mouth. They are also—you guessed it!—covered in tentacles. How novel.

In the RPG...

At first the Ny’ghan Grii seem like relative pushovers. They only have 4-point armour, their tentacles only do an average of 4 damage, and even their "Chilling Blast" magic attack only does an average of 2 damage per round. However, they have one other trick up their figurative sleeve. With an opposed POW roll—that it has a 71% chance of winning against an average human—a Ny’ghan Grii can make their target irrevocably devolve within an average of 7 rounds. That's a pretty nasty fate. In previous editions, this ability came with a magic point cost, which meant that its use was limited, but now that it's merely an opposed roll, it could be cast as often as the Keeper wants.

In a video game...

Despite their ability for what is essentially an insta-kill, I think Ny’ghan Grii would work in a video game. They're not that hard to take on, and perhaps the devolution ability could happen to an NPC when it was first encountered, just to strike fear into the player.

In a film...

I know nothing about Henry Kuttner's "The Invaders", but I can't see any reason a Ny’ghan Grii wouldn't work in a film. Seeing someone painfully devolving would be pretty horrifying, too.