Any Idea on how to make an ability that is only available after a set amount of left clicks ?

Hello ! I'm very very new to MCCreator. I've created a whip for myself with extended range (it was very very long.) and that's the only thing i made.

Today, i'd like to create a Gunblade mod. There is one already, but it doesn't suit what i'd like to have. 

If you ever happen to play FF14, that's my approach of it :
So i'd like to create that gunblade, with a set attack speed. And, after a number of left click, have a right click available, (perhaps turned on via a buff ? Or maybe by creating an ammunition after set number of clicks that can be kept & used for the right click would be the best but i don't think that's doable. idk how yet) the right click would be an ability that creates an explosion on the enemy hit. I have to find a way to make it destroy zero blocks and not hit the player too I suppose ?

Anyway if you think you have an idea on how to have an ability being usable after a set number of clicks that would be great ! (I'd need to have dumb explanations too, cause i'm so new to this)"