I'm not sure about the templating on this one, but I feel like the majority of the "game-rules" bears have had symmetrical effects (Meddling Mage, Gaddock Teeg, Kataki, etc.), so maybe
Judge of Time

Creature - Wizard
2/2
Each player skips his or her postcombat main phase.
"Better think twice before you attack..."
Or, if you want to keep the card such that it affects only opponents:
Judge of Time


Creature - Wizard
2/2
Each opponent skips his or her postcombat main phase.
"Better think twice before you attack..."
I do like the concept behind the card, though. My personal preference is for the second mod I posted--a 2/2 (you want a creature than can still attack while modifying the game state)--that affects all opponents.