Hidden Soldiers is a Normal 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, Hidden Soldiers is Unlimited.
YGOPRODeck lists Hidden Soldiers for these formats: OCG GOAT, Duel Links, Edison, Speed Duel, TCG, OCG, Master Duel.
A listed print of Hidden Soldiers appears in Legendary Collection 3: Yugi's World Mega Pack (LCYW-EN146) at Rare rarity.
Among markets shown on this page, the lowest listed snapshot for Hidden Soldiers is about $0.14 on TCGPlayer (prices change frequently).
