Referee Squad (MOM) from March of the Machine, available at 401 Games Canada.

• Rarity: Uncommon
• Finish: Normal
• Artist: Steven Belledin
• Card Text:
  Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for 1 or one mana of that creature's color.)
  Vigilance
  When Referee Squad enters the battlefield, tap target creature an opponent controls and put a stun counter on it. (If a permanent with a stun counter would become untapped, remove one from it instead.)