Leviathan, Tyrant of the Abyss

Islandwalk, Leviathan has Indestructible as long
as you control 5 islands
Morbid- Whenever another creature is dealt damage
by Leviathan and dies, put a flood counter on
Leviathan.

Whenever Leviathan deals damage to a player move
all flood counters from Leviathan onto defending
player, if a player has 7 or more flood counters at the beginning of the endstep, they lose the game.