Karn's Outburst

Signature Spell. This card can be your commander.
This card costs {2} additional mana for every time it
has been cast from your command zone.
You may have target player discard a card or sacrifice a permanent. You may copy this spell
up to X times, where X is the number of poison counter that player has, choosing new targets for
the copy. Then remove a poison counter from
players for each time this spell was copied.