Mirrodin Besieged is a rare Enchantment card from Modern Horizons (MH1), collector number 57. Current market price: $3.88 (foil $10.51), TCGplayer market prices via Scryfall.
As this enchantment enters, 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.