Mountain is a Field 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, Mountain is Unlimited.
YGOPRODeck lists Mountain for these formats: GOAT, Speed Duel, OCG GOAT, Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Mountain appears in Legend of Blue Eyes White Dragon (LOB-048) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Mountain is about $0.02 on Cardmarket (prices change frequently).
