Trap Stun 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, Trap Stun is Unlimited.
YGOPRODeck lists Trap Stun for these formats: Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Trap Stun appears in Astral Pack Two (AP02-EN013) at Super Rare rarity.
Among markets shown on this page, the lowest listed snapshot for Trap Stun is about $1.25 on Amazon (prices change frequently).
