Sludge Devourer

When Sludge Devourer enters the battlefield, destroy all lands, then put a +1/+1 counter on it for each land you controlled that was destroyed in this way.
Sludge Devourer has trample as long as it has seven or more +1/+1 counters on it.
Sludge Devourer has indestructible as long as it has ten or more +1/+1 counters on it.