Fortress Whale's Oath is a Ritual 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, Fortress Whale's Oath is Unlimited.
YGOPRODeck lists Fortress Whale's Oath for these formats: OCG GOAT, Speed Duel, Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
Fortress Whale's Oath belongs to the Umi archetype—use that tag when searching for engine pieces and tech options.
A listed print of Fortress Whale's Oath appears in Speed Duel: Scars of Battle (SBSC-EN016) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Fortress Whale's Oath is about $0.10 on Cardmarket (prices change frequently).
