Phyrexian Bolas, the Tyrant

Flying, infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
Whenever a player has five or more poison counters sacrafice Phyrexian Bolas, the
Tyrant and search your library for a Bolas planeswalker and put it onto the battlefield. Shuffle your library.