Mei

+1: gain 3 blue or 3 snow mana.
-1: Tap target creature, it does not untap until the player’s next untap step. It also gains +0/-3 until end of turn if you pay 3 X or 4 blue mana.
-7: Tap all creatures opponents control, they gain -1/-1 and do not untap during the opponent’s next untap step.