If I activate Jace's +1 effect "Until your next turn, whenever a creature an opponent controls attacks, it gets -1/-0 until end of next turn", do I have to designate just one creature or does it affect them all? And does it work against multiple opponents?
If any creature is coming at you it gets the neg, sorta like a wall of air. If 1 guy gets past, tge next ghy will have to try to pass the wall just the same. It works on all opponents until you go next
It works against all attacking opponents, in case you are thinking about multiplayer games.
So based on the ability text, if an opponent attacks another player, the attacking player's attacking creatures get -1/-0 until end of turn.
If you have an ally (2HG), that player is not your opponent and hence not affected.