Riryoku 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, Riryoku is Unlimited.
YGOPRODeck lists Riryoku for these formats: Speed Duel, OCG GOAT, Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Riryoku appears in Battle Pack 2: War of the Giants (BP02-EN142) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Riryoku is about $0.08 on Cardmarket (prices change frequently).
