Monstrous Onslaught (AER) from Aether Revolt, available at 401 Games Canada.

• Rarity: Uncommon
• Finish: Normal
• Artist: Slawomir Maniak
• Card Text:
  Monstrous Onslaught deals X damage divided as you choose among any number of target creatures, where X is the greatest power among creatures you control as you cast Monstrous Onslaught.