Tavern Brawl

At the beginning of each upkeep, sacrifice Tavern
Brawl unless there's a creature on the battlefield.
Creatures have vigilance, must attack each turn if
able, and cannot have or gain other abilities.
Whenever a creature dies, exile it.
When Tavern Brawl leaves the battlefield, return
all creatures exiled with Tavern Brawl to the battlefield tapped.