Magicians Unite is a Normal 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, Magicians Unite is Unlimited.
YGOPRODeck lists Magicians Unite for these formats: Speed Duel, Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Magicians Unite appears in Battle Pack 3: Monster League (BP03-EN152) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Magicians Unite is about $0.07 on TCGPlayer (prices change frequently).
