Oracle of the Herald 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, Oracle of the Herald is Unlimited.
YGOPRODeck lists Oracle of the Herald for these formats: Common Charity, TCG, OCG, Master Duel.
Oracle of the Herald belongs to the Herald archetype—use that tag when searching for engine pieces and tech options.
A listed print of Oracle of the Herald appears in 2015 Mega-Tin Mega Pack (MP15-EN176) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Oracle of the Herald is about $0.09 on Cardmarket (prices change frequently).
