What if we combined Evelynn's invisibility passive on her W?
Here are my thoughts, Evelynn's passive will in turn be changed to give back 1% of her total mana per basic attack.
Her new W would cost 40/45/50/55/60 mana. It would, when activated, turn her invisible, take away any and all slows, and she would gain 30/40/50/60/70% MS for 3 seconds. Any basic attacks during the 3 seconds will cause her to come out of invisibility. If Evelynn is hit, during the 3 seconds, she becomes visible. There is no 1000 perimeter to show when she is near. (Cool down can still be reset after a kill and can still be reduced by a second for each basic attack against a enemy champion.)