Licker (Resident Evil 2)
Why you wouldn't want to meet it up a dark alley: Curious mutation quirks aside (exposed brain? - duuh, that's a big help when it's raining) the Licker has a long, lance-like tongue that can penetrate a human torso. Which means it could have a taste of your liver while you're still alive. Yummers!
Movie monster we'd like to see it have a fight with...
Dougie, The Orderly Who Licks Sarah Connor's Face (Terminator 2: Judgement Day, 1991)
Who would win? Our money's on Dougie. Lickers are blind, while Dougie has massive, '80s, big-framed, bottle-bottom glasses to help him hunt down his prey.
He would give the Licker a taste of its own medicine by, umm, tasting its face. Then, as it blindly thrashed around its big taste-tentacle, trying to find him, Dougie would make it die by gently tapping its vulnerable brain with his riot baton, rolling his rheumy eyes in homicidal ecstasy.