Rethink 
Instant
Counter target spell unless its controller pays 
, where X is its mana value.
Legality
standardNOT LEGALpioneerNOT LEGALmodernNOT LEGALlegacyLEGALvintageLEGALcommanderLEGAL
Instant
Counter target spell unless its controller pays , where X is its mana value.