Cloak of Invisibility is a common Enchantment — Aura card from Mirage (MIR), collector number 58. Current market price: $0.22, TCGplayer market prices via Scryfall.
Enchant creature Enchanted creature has phasing and can't be blocked except by Walls. (It phases in or out before its controller untaps during each of their untap steps. While it's phased out, it's treated as though it doesn't exist.)