Swamp Stalker

When Swamp Stalker enters the battlefield, it becomes a basic Swamp land. Whenever a creature you control attacks, it gains Swampwalk. Whenever a creature an opponent controls attacks, if that player controls a swamp, exchange control of this creature and a random swamp that player controls. At the beginning of your end step, destroy a tapped creature you control at random. This ability only triggers if this creature is under control of a player who is not this creature's owner.