Sarkhan, Dragon Seeker

As long as you don't control a white or black permanent, Sarkhan has Vigilance.
{t}: add one mana of any color to your mana pool. Spend this mana only to cast a Dragon or Planeswalker spell.
At the beginning of your end step, if you contol two or more Dragons, destroy a non-Dragon creature you control and a non-Dragon creature you don't control. Then, exile Sarkhan, then return it under its owner's control transformed.