Hidden Armory 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, Hidden Armory is Unlimited.
YGOPRODeck lists Hidden Armory for these formats: Speed Duel, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Hidden Armory appears in Amazing Defenders (AMDE-EN041) at Rare rarity.
Among markets shown on this page, the lowest listed snapshot for Hidden Armory is about $0.05 on Cardmarket (prices change frequently).
