Necklace of Command is a Equip Spell Card.
Spell Cards are usually activated from the hand on your turn unless their type gives another timing window.
On the current TCG and OCG Forbidden & Limited lists tracked here, Necklace of Command is Unlimited.
YGOPRODeck lists Necklace of Command for these formats: GOAT, OCG GOAT, Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Necklace of Command appears in Dark Revelation Volume 3 (DR3-EN100) at Rare rarity.
Among markets shown on this page, the lowest listed snapshot for Necklace of Command is about $0.10 on Cardmarket (prices change frequently).
