Blightsteel Colossus

Search your library for a green creature card with mana value X or less, put it onto the battlefield, then shuffle. Shuffle Green Sun's Zenith into its owner's library.

Put X -1/-1 counters on each creature. Shuffle Black Sun's Zenith into its owner's library.

Choose one — • Slagstorm deals 3 damage to each creature. • Slagstorm deals 3 damage to each player.

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.) If damage would be dealt to this creature, prevent that damage. Put a -1/-1 counter on this creature for each 1 damage prevented this way.