Niv-Mizzet, the Firemind +Snake Umbra +

Infinite draw Infinite damage Revised by CR

Enchant Niv-Mizzet with Snake Umbra and tap him. Niv-Mizzet's ability will trigger, drawing a card, then dealing 1 damage to the opponent. Snake Umbra's ability will trigger, draw a card. Niv-Mizzet's ability will trigger again, dealing 1 damage to the opponent The loop will repeat until you draw your entire deck or Niv-Mizzet deals enough damage to the opponent.

Legallity