Sludge Serpent

Whenever Sludge Serpent attacks, Obliterate (To obliterate, put a ruin counter on target land. Lands with ruin counters on them can tap for only {c}. That land's controller may pay 2 life to remove the counter as a sorcery).
Sludge Serpent is unblockable as long as defending player controls at least two lands with ruin counters on them.