I'll take a stab at this:
Here is my current iteration of the mechanic.
Grolla uses a new mechanic known as Souls. She receives a Soul every time she kills a unit, up to a maximum of three, also replenishing part of her supply of Souls if she remains out of combat for an extended period of time. Every time she uses one of her basic abilities, she expends a Soul. Her abilities do not require Souls to be cast, but if used without Souls, they will be significantly weaker.
|Grolla also has a unique, optional item she can purchase called the Seyfarth Soul Gem, which augments her mechanics. It adds bonus magic damage to her basic attacks based on her level and the number of Souls she has, and increases the maximum number of Souls she can carry by one. It also can be activated to instantly give Grolla two additional Souls (2 minute cooldown), which can be useful in heated fights.|
Grollschwert (innate passive)
Every time Grolla kills an enemy minion or monster, she receives 1 Soul. Killing enemy Champions gives Grolla 2 Souls, while assists give her 1 Soul. Whenever Grolla uses a basic ability, she consumes a Soul if she has one, enhancing its effect. If Grolla remains out of combat for 10 seconds, she will reset her Soul count to 1. Grolla can hold a maximum of 3 Souls at a time (4 if she has the Seyfarth Soul Gem).
For every Soul Grolla has, she receives 3/6/9/12 bonus AD. (Increases at levels 6, 11 and 16)
However, +AD for his resource is not great. Basically, you're telling the player he's nerfing himself by using abilities. This has a lot of impact: He'll want to always open with his highest AD-ratio ability even if it's not the right play, and he'll often want to not hit abilities at all in favor of just landing basic attacks.