It all started about three years back when a bit of poisoned fish fell into the Atlantic off of a spy-boat amidst a conflict with the Mafia, but that's an entirely different story.

Anyway, that bit of poisoned fish ended up as lunch for a small flounder on the east coast of the United States. After that fateful meal, the flounder began to grow and mutate, and he got hungrier and hungrier. He began to take short trips out of the water to eat whatever he could find, until he stopped returning to the water altogether. His appetite expanded, and he found a favorite food in people, using his flat body to slip behind doors and hide under beds where nobody can see him...

(Made for the Monster in the Closet skin contest.)