WoW API < UnitMana

Returns the mana points of the specified unit. DEPRECATED - As of 3.0, UnitPower is the preferred method of obtaining unit power.

local mana = UnitMana("unit");

String - The UnitId of the unit whose MP should be returned

Number - the unit's current mana points

There's nothing special about this really. There is, however, one interesting anomally: While UnitHealth will return percentage values for "target" and "mouseover", this one seems to return the actual mana points for all possible targets.
This is also the mechanism for getting a unit's rage or energy, since there were no corresponding UnitEnergy or UnitRage functions. You can use UnitPowerType to figure out whether what you're getting is Rage, Energy, or actual Mana.
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