Surprised no ones found this yet.
Anyways I've found out how to charge attacks.
You want to use variables.
Infact, you want to use a random access float variable.
To add one, put in the event 12060200.
Leave value where it is.
Variable set to random access float.
Add a number 150+ (this'll stop conflicts).
In the "charge" subaction add the event 12070200.
Change value to how much will be added.
Change variable to the previous variable.
Now.
If you want the variable to increase damage.
It's simple.
Make a hitbox, in damage change value to variable, then add the variable
I'm messing around with this right now, I think i've found how to max out the charge.
ENJOY, I know I will
EDIT: The event set float variable( changing the value to 0) changes the "charge" to 0.