Banner of Courage is a Continuous 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, Banner of Courage is Unlimited.
YGOPRODeck lists Banner of Courage for these formats: GOAT, OCG GOAT, Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Banner of Courage appears in 2-Player Starter Deck: Yuya & Declan (YS15-END15) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Banner of Courage is about $0.07 on TCGPlayer (prices change frequently).
