Magic: The stat needed to use spells. Decreases when spells are used, but recovers over time.
Literal
Magic-power (Magic): magic [object-を] use [purpose-ために] necessary stat-value. Magic [object-を] use-[conditional-と] decrease [but-が], time [with-で] recover.
A game stat description. 能力値 'stat value' — RPG terminology. 魔力 'magic power' with the English gloss Ｍａｇｉｃ in fullwidth letters. 減少する 'to decrease' and 回復する 'to recover' are standard game terms. The colon-delimited format is typical of game manuals.