Teferi's Veil is a uncommon Enchantment card from The List (PLST), collector number WTH-53. Current market price: $1.46, TCGplayer market prices via Scryfall.
Whenever a creature you control attacks, it phases out at end of combat. (While it's phased out, it's treated as though it doesn't exist. It phases in before you untap during your next untap step.)