DISCLAIMER: Fullmetal Alchemist belongs to Hiromu Arakawa. The Nightmare Before Christmas belongs to Tim Burton.

A/N: Yes, the punchline is dumb and obvious, and the title is a Yu-Gi-Oh card, for that extra little layer of crackiness.

~ Polymerization ~

Edward and Alphonse Elric chalked the transmutation circle carefully on the floor, then placed the items they'd brought at strategic points within it.

"But, Brother, what will get if we combine coffee, Halloween, and a trashy mask?" Al asked worriedly.

"Shut up, and concentrate!" Ed snapped.

The sentient suit of armor whimpered.

They both put their hands down along the edges of the transmutation circle and activated it.

Light flooded the room, and when it cleared, the transmutation circle and its contents had disappeared, replaced by a strange black door. A door which was embedded directly in the floor.

The door opened and Jack Skellington popped out.

"What's this?" Jack shouted excitedly.

Ed and Al screamed like girls and ran away.

~end~