Mage Power 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, Mage Power is Unlimited.
YGOPRODeck lists Mage Power for these formats: GOAT, OCG GOAT, Duel Links, Speed Duel, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Mage Power appears in 2-Player Starter Set (STAS-EN028) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Mage Power is about $0.13 on Cardmarket (prices change frequently).
