Rekindling 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, Rekindling is Unlimited.
YGOPRODeck lists Rekindling for these formats: Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Rekindling appears in Ancient Prophecy (ANPR-EN060) at Short Print rarity.
Among markets shown on this page, the lowest listed snapshot for Rekindling is about $0.10 on Cardmarket (prices change frequently).
