Magus of Lost Identities

Magus of Lost Identities enters the battlefield as a copy of another creature on the battlefield except it gains "Whenever this creature deals combat damage to a player who controls a creature with the same name as this creature, that player mills 5. (They put the top five cards of their library into their graveyard)"
When Magus of Lost Identities is put into your graveyard from the battlefield, return it to it's owner's hand.