Sylo, Prince of Phyrexia

Haste, Flying
You may cast Sylo, Prince of Phyrexia from exile
and your graveyard long as you have a poison
counter.
Whenever a creature dies, put a +1/+1 counter
on Sylo, Prince of Phyrexia.
Counters remain on Sylo, Prince of Phyrexia as it
moves to any zone other than a player's hand or library.