I fielded the Duck of Doom once (a Munchkin card-game reference)
If touched or attacked, there is a d100 chart to see what awful things happen (from the Munchkin Monster Manual) 100 was a rend in spacetime.
"never pick up a duck in a dungeon!"
I also once had a T-Rex rider. But the rider died early on in the game, and the T-Rex became an independent unit, not under control of any army general. Instead, it sought out the smell of blood, and attacked any moving object in line of sight. An entire squad of archers were wiped out before they could take it down.