Ward of Bones 
Artifact
Each opponent who controls more creatures than you can't cast creature spells. The same is true for artifacts and enchantments. Each opponent who controls more lands than you can't play lands.
Legality
standardNOT LEGALpioneerNOT LEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL