Mavin's Create Volcano

Enchant Target Mountain.
When Mavin's Create Volcano enters the battlefield, put three time counters on enchanted permanent.
Enchanted mountain has Hexproof.
At the beginning of your upkeep, remove a time counter from Enchanted Permanent.
At the beginning of each phase, Mavin's Create Volcano deals 20 damage to each permanent and destroy each other Artifact or Enchantment.