Chthonian Alliance is a Equip 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, Chthonian Alliance is Unlimited.
YGOPRODeck lists Chthonian Alliance for these formats: Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Chthonian Alliance appears in Dark Revelation Volume 4 (DR04-EN104) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Chthonian Alliance is about $0.07 on Cardmarket (prices change frequently).
