Clear the Board

Whenever Karn blocks or becomes blocked, it gets -4/+4 until end of turn. : Target noncreature artifact becomes an artifact creature with power and toughness each equal to its mana value until end of turn.

: Target spell or permanent becomes the color of your choice until end of turn.

: Untap target artifact creature.

: Add three mana of any one color.

Return all permanents of the color of your choice to their owners' hands.

(: Add .)