Mesmeric Orb (Retro Schematic) (Serialized) [The Brothers' War Retro Artifacts] SWSH185 prevent 1 arcane damage that

prevent 1 arcane damage that source would deal

Set: Promo Finish: Cold Foil Type: Instant Rarity: Promo Class: Runeblade Cost: 0 Destroy an aura permanent with cost X or less and/or up to X aura tokens

—The Underworld Cookbook

(It's an aura with "When you play an attack action card or attack with a weapon

Mesmeric Orb (Retro Schematic) (Serialized) [The Brothers' War Retro Artifacts] SWSH185 prevent 1 arcane damage thatSet: The Brothers' War Retro Artifacts Type: Artifact Rarity: Mythic Cost: {2} Whenever a permanent becomes untapped, that permanent's controller mills a card. "I now believe the strange orb was some kind of Thran security device. Supporting this hteory, I can no longer recall where I found it." Tocasia, journal entry