Carnifex

{x}{b}{r}{g}: Monstrosity X. (If this creature
isn't monstrous, put X +1/+1 counters on it and
it becomes monstrous.)
When Carnifex becomes monstrous, destroy
all other nonland permanents. For each permanent destroyed this way, its controller searches their library for a basic land and
puts it on the battlefield tapped. Shuffle afterwards.