Cankerous Thirst (EVE) from Eventide, available at 401 Games Canada.

• Rarity: Uncommon
• Finish: Normal
• Artist: Carl Frank
• Card Text:
  If B was spent to play Cankerous Thirst, you may have target creature get -3/-3 until end of turn. If G was spent to play Cankerous Thirst, you may have target creature get +3/+3 until end of turn. (Do both if BG was spent.)