As Mirrodin Besieged enters the battlefield, choose Mirran or Phyrexian.
- Mirran - Whenever you cast an artifact spell, create a 1/1 colorless Myr artifact creature token.
- Phyrexian - At the beginning of your end step, draw a card, then discard a card. Then if there are fifteen or more artifact cards in your graveyard, target opponent loses the game.