Attack that also buffs the user

I feel like this is something I should be able to figure out on my own (actually, I sorta feel like I did figure it out once), but I'm pretty rusty.

In short, I want to make a skill that attacks an enemy, but also applies a buff/debuff to the user. For instance, there are games that have a skill that is a strong attack, but then lowers the user's ATK afterward. That kind of thing.

I have a common event that adds a buff to the entire party and attach it to the skill; you can do the same thing but use the Script... function and add, for example, "a.addBuff(6, 5) which adds an agi buff for 5 turns.

Stat buff numbers in the formulas "a.addBuff(x, y)" and "b.addDebuff(x, y)", where x is the stat and y is the number of turns, run as follows:

0 - maximum HP
1 - maximum MP
2 - Attack
3 - Defense
4 - Magic Attack
5 - Magic Defense
6 - Agility
7 - Luck

If you want to add a specific state to the actor, put this before your damage formula:
Where x is the number of the state you want to add.

Example:

Will add state 13 to the user and deal damage equal to 4 times user attack minus defenders defense.

Make a state, define the buff/debuff properties on said state and of course turn duration.

Personal opinion/suggestion starts here!
Set no icon/overlay/motion if you dont want to but to be honest if the attack has an upside/downside better let the player know, making users memorize "hidden" skill effects off a description they will read only once they get the skill and a few times later until they get used to it will be annoying when the skill selection expands, moreso if you add even more skills with "hidden" effects (= ω=)...
Personal opinion/suggestion ends here!

Well once the state is done you either add it on the attack formula since its a self inflicted effect (iirc the "attack effect" box is to inflict states on the skill target), or in the case of any action animation system (yanfly, victor engine, etc), add it on the notetags with its proper syntax.

For adding it on the attack formula:
a.addState(X); normal damage formula here

Where X is the state number (position on the list) in your database.