Resonator Engine 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, Resonator Engine is Unlimited.
YGOPRODeck lists Resonator Engine for these formats: Duel Links, Common Charity, TCG, OCG, Master Duel.
Resonator Engine belongs to the Resonator archetype—use that tag when searching for engine pieces and tech options.
A listed print of Resonator Engine appears in Ghosts From the Past (GFTP-EN114) at Ultra Rare rarity.
Among markets shown on this page, the lowest listed snapshot for Resonator Engine is about $0.03 on TCGPlayer (prices change frequently).
