Synthesis Spell is a Ritual 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, Synthesis Spell is Unlimited.
YGOPRODeck lists Synthesis Spell for these formats: Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Synthesis Spell appears in Strike of Neos (STON-EN043) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Synthesis Spell is about $0.19 on TCGPlayer (prices change frequently).
