Rat People

Once human, Rat People have degenerated to a near animal state. I get the impression from their write-up in the old Malleus Monstrorum that they are even less human than those pictured below, as it says that they sometimes walk on all fours and has no mention of weapons or even clothing.

In the RPG...

There are two traits of note for Rat People. The first is that a bite from one can carry disease—upon a failed CON roll. Untreated, this disease has the potential to cost the investigator 30 CON and 6 hit-points over 3 days, though these can be restored by either Medicine rolls or bed-rest. The other trait of note is that a Rat Person's bite cannot be healed naturally, as in, the hit-point loss is permanent.

In a video game...

In a video game context, the disease would have to have a much more immediate effect. Aside from that, I think Rat People would make for a good bottom-tier enemy to be encountered when the player is in places that normal rats might be seen.

In a film...

I can't think of any off-hand, but I'd be very surprised if some kind of anthropomorphic rat hadn't already been seen in a horror movie. These creatures are taken from Lovecraft's story The Rats in the Walls, and I think the ending to that story would be amazing on the big-screen.