Sivvi's Ruse 
Instant
If an opponent controls a Mountain and you control a Plains, you may cast this spell without paying its mana cost. Prevent all damage that would be dealt this turn to creatures you control.
Legality
standardNOT LEGALpioneerNOT LEGALmodernNOT LEGALlegacyLEGALvintageLEGALcommanderLEGAL