Hero Mask 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, Hero Mask is Unlimited.
YGOPRODeck lists Hero Mask for these formats: Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
Hero Mask belongs to the Elemental HERO archetype—use that tag when searching for engine pieces and tech options.
A listed print of Hero Mask appears in HERO Strike Structure Deck (SDHS-EN027) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Hero Mask is about $0.07 on Cardmarket (prices change frequently).
