Guts of Steel 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, Guts of Steel is Unlimited.
YGOPRODeck lists Guts of Steel for these formats: Duel Links, Speed Duel, TCG, OCG, Master Duel.
A listed print of Guts of Steel appears in Duelist Revolution (DREV-EN086) at Rare rarity.
Among markets shown on this page, the lowest listed snapshot for Guts of Steel is about $0.20 on Amazon (prices change frequently).
