Lavafields

You may decide not to untap Lavafields during your untap phase.
{t} to prevent an attacking creature from dealing damage this turn. This creature doesn`t untap as long as Lavafields remains tapped. At the beginning of your untap phase put a counter on Lavafields. Targeted creature takes two points of damage for every counter on Lavafields. Remove all counters from Lavafields when untapping it.