Mox Opal [Double Masters] Cat Nightmare Beast If a Spell/Trap Card is

If a Spell/Trap Card is activated in this card's column: You can Special Summon 1 Level 4 or lower "Magical Musket" monster from your Deck in Defense Position

Set: Generation Force Card type: Xyz/Effect Monster Rarity: Ghost Rare Attack: 2000 Defense: 0 2 Level 3 monsters Once per turn: You can detach 1 Xyz Material from this card

it's treated as though it doesn't exist

Set: EX: Holon Phantoms Type: Lightning Rarity: Uncommon Retreat cost: Colorless

and many others

Mox Opal [Double Masters] Cat Nightmare Beast If a Spell/Trap Card isSet: Double Masters Type: Legendary Artifact Rarity: Mythic Cost: {0} Metalcraft {T}: Add one mana of any color. Activate this ability only if you control three or more artifacts. The suns of Mirrodin have shone upon perfection only once.