The Flea

When The Flea enters the battlefield choose two creatures controlled by the same player. Those creatures cannot attack or block unless both are able and do so.
If both creatures leave the battlefield, destroy The Flea. If one of the creatures leaves the battlefield, destroy the other creature and The Flea. If The Flea leaves the battlefield, destroy both creatures. If they are ever controlled by different players, destroy both of them and The Flea.