Supervise 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, Supervise is Unlimited.
YGOPRODeck lists Supervise for these formats: Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Supervise appears in Legendary Decks II (LDK2-ENJ31) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Supervise is about $0.12 on TCGPlayer (prices change frequently).
