Arrow Volley Trap (ZEN) from Zendikar, available at 401 Games Canada.

• Rarity: Uncommon
• Finish: Normal
• Artist: Steve Argyle
• Card Text:
  If four or more creatures are attacking, you may pay 1W rather than pay Arrow Volley Trap's mana cost.
  Arrow Volley Trap deals 5 damage divided as you choose among any number of target attacking creatures.