Avacyn's Collar, the Symbol of Her Church is a rare Artifact — Equipment card from Mystery Booster 2 (MB2), collector number 509. Current market price: $0.22, TCGplayer market prices via Scryfall.
Equipped creature can't attack, block, or transform, and its activated abilities can't be activated. Shackle {3} ({3}: Attach to target creature you don't control. Shackle only as a sorcery.)