Sluggishness is a common Enchantment — Aura card from Urza's Legacy (ULG), collector number 92. Current market price: $0.15 (foil $1.80), TCGplayer market prices via Scryfall.
Enchant creature Enchanted creature can't block. When this Aura is put into a graveyard from the battlefield, return it to its owner's hand.