Here...
I'm using GDD to make it work.
There are a JASS version and a GUI version on this map.
Do have in mind, that if you aren't using GDD, you'll need to change some variables to make the "OnDmg" trigger work.
(I was thinking to make a built-in DDS for this skill, but decided not to make it too complicated, as you most likely already have a DDS on your map)
View attachment 152301
Describtion of how it works on this sample map:
1) When a unit uses the Charge-up strike - it checks if its the 1-st time the unit has used it.
a) if it is - it sets the "times used" to 1
b) if it's not - it sets the "times used" to +1
2) 60 seconds after the 1-st time the skill is used. If the effect hasn't been used - the bonus dmg and the buff are removed.
3) If a the buff is dispelled - you lose the bonus dmg from it.
4) When you damage a unit, while you have the buff - the buff it removed, the dmg bonus is nullified, and you deal bonus damage equal to 3+(times charged up). You can easily configure the bonus damage in the GUI version (in the JASS one too, if you know JASS)
NOTES:
I) You do NOT see the bonus damage anywhere.
II) You do NOT see time remaining for the buff.
Tell me if you want these "fixed".
( I could fix (I) in 2 ways: make it give you a "green" bonus damage in the damage field // OR // when the unit deals damage - display the bonus damage with a floating text ;
While I could fix (II) by adding a timer window, showing how much time remains)