King Scarlet is a Continuous Trap Card.
Trap Cards are normally Set first and can be activated on a later turn, often in response to an action.
On the current TCG and OCG Forbidden & Limited lists tracked here, King Scarlet is Unlimited.
YGOPRODeck lists King Scarlet for these formats: Duel Links, Common Charity, TCG, OCG, Master Duel.
King Scarlet belongs to the Archfiend archetype—use that tag when searching for engine pieces and tech options.
A listed print of King Scarlet appears in 2017 Mega-Tin Mega Pack (MP17-EN109) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for King Scarlet is about $0.07 on Cardmarket (prices change frequently).
