I once built one called Night of the Living Deck that was fully populated with zombie cards. It built out a cheap creature army and then relied on getting a card that turned a target land into a Swamp. Zombies had swamp walk, so at that point the entire army could march past the defenders and just wipe the opponent.

I built it as a joke but it actually played pretty well and won a decent number of times. The best part was how angry people would get from losing to such a basic deck.