How to fix Evelynn
By fix I don't mean that they are OP, but that she always walks that fine line between just being good enough to be playable, or too strong because of her permanent invisibility.
So, tell me if I'm way off base here, but this is what might be a good fix.
Give her bleed damage, but reduce the base damage she does with her abilities. Basically, like a Darius style ability, but catered to Eve.
Why does this make sense? Well, a couple reasons.
First, she's a vampire... sorta. They imply she's a vampire anyways.
Secondly, this gives her counterplay and power at the same time. Don't want to die? Don't let her get stacks on you. When she gets fed she can still run around the map, pop out of nowhere, add bleed stacks to someone and kill them.
In summary, the way to do this would be to add a stacking bleed in magic damage to her E and her ultimate. She can do more damage on bleeding targets via each stack makes the bleed tick for more and works solidly with death fire. The ultimate could still do what it currently does, but add bleed stacks to enemies hit.
She wouldn't be losing or gaining any actual total damage this way (just moving it over into a stacking debuff), but it thematically makes more sense and lets her be the invisible assassin she's supposed to be without breaking her. Plus.. you know.. she makes spikes everywhere. You bleed when you get hit by spikes!
Unless you're a robot. 