Veiled Apparition is a uncommon Enchantment card from Urza's Saga (USG), collector number 107. Current market price: $0.21, TCGplayer market prices via Scryfall.
When an opponent casts a spell, if this permanent is an enchantment, it becomes a 3/3 Illusion creature with flying and "At the beginning of your upkeep, sacrifice this creature unless you pay {1}{U}."