Doomsday

Doomsday cannot be the target of more than one instance of the same card type each turn (card types are Instant, Sorcery, Creature, Enchantment, Land, and Planeswalker).
If lethal damage would be dealt to Doomsday, instead put a +1/+1 counter on Doomsday and tap it. It does not untap as usual next turn.
{b}, Discard a card: return Doomsday from your graveyard to the top of your library.