7 Completed 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, 7 Completed is Unlimited.
YGOPRODeck lists 7 Completed for these formats: GOAT, OCG GOAT, Speed Duel, Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of 7 Completed appears in Battle Pack 3: Monster League (BP03-EN135) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for 7 Completed is about $0.08 on Cardmarket (prices change frequently).
