You hear an odd sound like a wet, claw like heavy like sound very slowly approaching

SCULK, KLUK, KILK, KARK (sound it makes when it crawls)

You see a half-human, half-fish monster with flabby blue skin, a large mouth full of sharp teeth, long unkempt black hair, and a blowhole on its back.

it's crawling towards you & it's slow also very ugly.