Here is the full list of all 38 Halloween Forever achievements.
Beat the game with 1 HP Mode enabled! HARDCORE!!!
Never harm little bats! Ever!
Get grabbed by Blue Devil three times.
You won as Pumpkin Man! Get pumped!
Run away from a crow for a very long time.
Watch Manleech vomit 10 times. Yucky!
Beat a world without taking a hit.
You won as Ms. Witch! Hope you had a feline time.
Set loose 666 cats as Ms. Witch.
You won as Butternut Bro! Way to squash the opposition.
Find all six hidden runes for a secret ending!
You rescued Ms. Witch! She has endless cats!
You won as A Skeleton! I knew you had it in you (I can see through your ribgaps).
You bested Necroking! The return of Necromancer! How the mighty have fallen.
You bested Blue Devil! Necessity is the moth of invention.
You bested Frog King! I toad you so!
You bested Manleech! Say your lamprey-ers!
Wake up 6 sleepy frogs.
You bested Necromancer! Back to ghoul school with you, fool!
Knock five spiders off the wall.
You bested Eyeskuller! Eye spy with my little eye something that's about to explode!
Trigger spike traps 101 times.
You bested Red Devil! Yow, it's hot in here!
You rescued A Skeleton! A bony vertebra buddy.
You bested Green Hydra! Two heads are better than none, but that won't slow us down.
Destroy five hanging skeletons before they hit the ground.
You bested Big Bat! Have you ever seen a bat so big?
Make Chainsaw Megamaniac leave his chainsaw behind when he dies.
You rescued Butternut Bro! Your gourd from another lord.
You bested Chainsaw Megamaniac! There's no chainsaw maniac tougher than this one.
Destroy a breakable wall.