I think you don't really understand what the npc->Damage function does.
It really has nothing to do with spell casting, in the source it is used to apply the damage of the spell after its been fully calculated out based on the spells data. When used as a quest function its nothing more then sending a message and some graphics.
You can't just make fake buffs using quest functions. The entire spell process relies on pulling data from the spells_new table that is loaded into memory.
It is not impossible to add what you want but it is just such a narrow application requiring a lot of custom code it i just isn't justified.
Especially since there is a very simple and straight forward solution to what you want to do using the existing mechanics.
Just make several different custom rune spells with increasing amounts.
Then when a player casts a spell based on what the heal amount is ect
Use $mob->SpellFinished to apply the rune effect using the custom spell id.
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