Surtr, Guard of Muspell

When Surtr enters the battlefield, sacrifice any number of lands you control. Target opponent sacrifices up to X lands where X is the number
of lands you sacrificed. For the difference of X minus the number of lands target opponent sacrificed, deal X damage to that many targets.
Surtr's power and toughness is equal to double
the number of X minus the number of lands target opponent sacrificed.
"Twilight of the Gods"