Unnerving Assault [Eventide]

Set: Eventide Type: Instant Rarity: Uncommon Cost: {2}{U/R} Creatures your opponents control get -1/-0 until end of turn if {U} was spent to cast this spell, and creatures you control get +1/+0 until end of turn if {R} was spent to cast this spell. (Do both if {U}{R} was spent.) The scales of battle rarely balance.