Priest · Discipline · tier 3 · from level 20

Mental Agility

+22.9 Renew

3/3 · level 60 · per 100 mana · and 8 more

Mental Agility 123

Rank 3/3

Reduces the mana cost of your Smite, Holy Fire, and instant cast spells by 10%.

Renew +11.1% +22.9 Power Word: Shield +11.1% +20.6 Shadow Word: Pain +11.1% +17.6 Holy Fire +11.1% +12.0 Prayer of Mending +11.1% +12.0 Devouring Plague +11.1% +9.3 Smite +11.1% +6.8 Holy Nova healing +11.1% +4.7 Holy Nova +11.1% +2.7

Averages, counting crits and misses, for a level 60 Priest with a typical weapon and no other gear or buffs, against a target your level. Worked out from the game's own data, the same way as the Foresight addon.