Ekko's Positioning
Its really really cool. When he goes in or initiates he typically will loose a lot of hp. But if he procs his passive on the right champion, he can get away albeit with low hp.
Whats really cool, at least to me, is that he can then stay on the outside of the fight after the initial engage and make a real contribution in the cleanup phase with his q and his e if he needs to, or he can run if it goes bad.
Thats really cool decision making.