Soul Unseal 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, Soul Unseal is Unlimited.
YGOPRODeck lists Soul Unseal for these formats: OCG.
Among markets shown on this page, the lowest listed snapshot for Soul Unseal is about $3.00 on eBay (prices change frequently).
