<Custom Regenerate Effect>
var = This is creating a "variable" and attaching a number to it based off the formula.
In the (ENTER FORMULA HERE) spot, you could put in whatever you want, for example, if you wanted it to be a flat 5, just put a 5.
You can do more complex things in the formula as well, such as: Math.round(user.mmp * 0.03 + 5); which takes 3% of the user's Maxmp and adds +5 to it.
var mpheal = (ENTER FORMULA HERE);
This section here is what is actually healing the MP to the user. The stuff in the parenthesis is calling the "var" (variable) formula from above.
user.gainMp(+mpheal );
This starts the popup on the actor, that way the player can visually see that this actor got some MP.
user.startDamagePopup();
This clears the combat log (the little black box that says things like "Actor A took 5 damage!" etc)
user.clearResult();
</Custom Regenerate Effect>