Evelynn and a "Pain meter"

So, I realize that what Evelynn actually is, is still up for debate. But, I've been thinking about Evelynn's concept of thriving off of pain, and that led me to the idea of her having something in her kit that scaled with how much damage she has done to champions (and or taken).

At first I thought of a meter that filled every time Evelynn received or dealt damage, and once filled she could empower one of her abilities (Example: Empowerd Ravage: Evelynn strikes her target an additional 2 more times, and causes a bleeding effect that deals damage based off missing health)

But I quickly realized that it sounds a bit too similar to Renektons Rage meter. And then I got to thinking "Well, what if she had an ult that scaled off how much damage she has dealt (And or received?) throughout the game?" I don't have the slightest clue what an ult like that would look like, nor how it would need to be balanced. But I really think something interesting could come form this concept of "thriving off pain", something that hasn't been done in League yet. What are your guys (Evelynn players) thoughts?