All-Seeing Arbiter - Promo Pack (PSNC) from Streets of New Capenna, available at 401 Games Canada.

• Rarity: Mythic Rare
• Finish: Normal
• Artist: Robin Olausson
• Card Text:
  Flying
  Whenever All-Seeing Arbiter enters the battlefield or attacks, draw two cards, then discard a card.
  Whenever you discard a card, target creature an opponent controls gets -X/-0 until your next turn, where X is the number of different mana values among cards in your graveyard.