Etrata, the Taker

Unblockable, hexproof
When Etarata deals damage to a player, gain control of target permanent and put a gain counter on it, then, shuffle Etrata into its owner’s library.
When Etrata is put into a graveyard, each player gains control of all the permanents they control with hit counters on them, then, if a player controls 3 or more permanents with hit counters, they lose the game