Frontline Base is a Continuous 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, Frontline Base is Unlimited.
YGOPRODeck lists Frontline Base for these formats: GOAT, OCG GOAT, Duel Links, Speed Duel, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Frontline Base appears in Dark Revelation Volume 1 (DR1-EN083) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Frontline Base is about $0.04 on Cardmarket (prices change frequently).
