Dark Snake Syndrome 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, Dark Snake Syndrome is Unlimited.
YGOPRODeck lists Dark Snake Syndrome for these formats: GOAT, OCG GOAT, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Dark Snake Syndrome appears in Dark Revelation Volume 1 (DR1-EN035) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Dark Snake Syndrome is about $0.30 on TCGPlayer (prices change frequently).
