Kalista's Passive Martial Pose
Problem: Kalista's passive is essentially Ezreal's E, except with 0CD, instant cast and no drawbacks (ignores most CC). This makes getting in range incredibly hard, makes it extremely easy to kite people and makes landing skillshots on her nearly impossible. She is widely considered one of the two or three best ADCs in the game, far above most others.
Solution: Give Kalista's passive an internal CD of 3-4 seconds, so that she cannot constantly hop, but rather must use each hop tactically and as a dodge or a maneuver, rather than a perma "You can't touch me!" ability.