Flash Fusion is a Quick-Play 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, Flash Fusion is Unlimited.
YGOPRODeck lists Flash Fusion for these formats: Duel Links, Common Charity, TCG, OCG, Master Duel.
A listed print of Flash Fusion appears in Dragons of Legend (DRLG-EN016) at Super Rare rarity.
Among markets shown on this page, the lowest listed snapshot for Flash Fusion is about $0.08 on Cardmarket (prices change frequently).
