SCP-173

This creature enters the battlefield under no
player's control (this creature has no controller).
Indestructible
At the beginning of each end step, SCP-173
fights each tapped creature.
At the beginning of each upkeep, untap this creature, then if that player controls no untapped creatures, SCP-173 attacks that player.
Object Class: Euclid [Sentient and Violent]