Swamp Hydra of the Bog

Swamp Hydra of the Bog enters the battlefield with X +1/+1 counters on it
Islandwalk, swampwalk, deathtouch
When Swamp Hydra of the Bog enters the battlefield, each player puts the top 4 cards of their library into their graveyard
When Swamp Hydra of the Bog leaves the battlefield, each player loses 2 life