Gulla Void-Mantle

When Gulla Void-Mantle enters the battlefield,
each player Mills X, where X is the total amount
of mana spent to cast Gulla Void-Mantle.
Remove from the game all lands that would enter
a graveyard from anywhere other than exile.
{t}, Choose up to X target lands in exile and
put them into their owner's graveyard:
Create an X/X Illusion creature token
with skulk, then Surveil X.