Strangling Spiral

Protection from green
{g}: Tap target permanent.
{g}{g}, Discard a card: Destroy target artifact or enchantment.
{g}{g}{g}, Discard a card: Destroy target creature.
At the beginning of your end step, if you have 12 or more cards in your graveyard, transform Strangling Spiral.
Deprived of sustenance, these otherwise benevolent vines go berserk, crushing and strangling anything they can wrap themselves around.