Crystal Cavern

Crystal Cavern enters the battlefield tapped with three crystal counters on it.
{t}: Add one mana of any color to your mana pool. Then flip a coin. If you win the flip, create a 1/1 white beast with haste. It gets double strike or lifelink until your next end step. Otherwise, Crystal Cavern deals 2 damage to you.
{3}, Remove a crystal counter from Crystal Cavern: you gain 2 life and create a 2/2 green beast with trample.