Greatwurm of Urborg

When Greatwurm of Urborg enters the battlefield, sacrifice any number of lands.
For each Forest sacrificed this way, put a
+1/+1 counter on each creature you control.
For each Swamp sacrificed this way, put a
-1/-1 counter on each creature your
opponent controls.
{b/g}: Regenerate Greatwurm of Urborg.