Variable ability power

This does NOT mean the power varies on its own (though it can also vary on its own in addition to this), but rather with player control of it (e.g. selecting how much more magic points to expend on it beyond the minimu, or which power level out of 5 to use). Nor does this include variable power achieved from designing the spells at different power levels. Nor does this include leveling up the actual spells themselves (so you no longer can cast the lower level spells).

Variations:
* Power level - player designates the power at which to cast the spell at
* Mana feed - player designates how much more mana (magic points) to use on the spell besides the minimum necessary

Depending on the game, the power level or mana feed may be remembered, either in some spell shortcut or in the spell itself.