Bjorn Frostbeard

Whenever a land enters the battlefield under an opponent's control you may tap a number of
untapped dwarves you control equal to the
number of lands that opponent controls. If you
do, put 5 depletion counters on the land that
entered the battlefield.
Whenever a land is tapped for mana, if it has a
depletion counter on it, remove a depletion
counter. When the last depletion counter on a
land is removed, that player sacrifices that land.