Mysterious Triangle is a Quick-Play 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, Mysterious Triangle is Unlimited.
YGOPRODeck lists Mysterious Triangle for these formats: Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
Mysterious Triangle belongs to the Alien archetype—use that tag when searching for engine pieces and tech options.
A listed print of Mysterious Triangle appears in Crimson Crisis (CRMS-EN062) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Mysterious Triangle is about $0.04 on Cardmarket (prices change frequently).
