Add Buff Function

Is there "Add Buff Function" which would add a buff (any) to unit or unit group!

I want to do that with trigger action
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I would also apreciate if you could explain what each part of function does.
Thanks!

AFAIK, there is only the dummy caster method via spells to apply buffs on units (except very specific ones).

How does this dummy caster method work?

make a caster have the ability that has the buff, then order the caster to use that spell.

I don't know about adding buffs specifically, but I know UnitRemoveAbility can get rid of them. Also, the Unit Has Buff check is essentially an encapsulated form of GetUnitAbilityLevel. This, to me, strongly suggests buffs are simply a form of ability you can add and remove like any other- though whether you'd get any accompanying spell effects is another matter- I doubt it. Try messing about with this.

You're right that you can detect and remove buffs using the ability related functions. Though, UnitAddAbility cannot add buffs for some reason.

I know for Unit - Remove Buff function and functions similar to this one.
But that's not what I need.
I tried dummy caster and it was ok!
Thanks!