Ekko - Minor Tweaks
I only see a few issues left with this champion, and not all of them are over powered (Also, I'm merely listing ideas off of the top of my head for these things, if any one else has some please share, I am not stuck on any particular idea concerning any of these):
Passive - Z-Drive Resonance This Movement Speed increase for hitting a champion ultimately grants him an escape from a tower dive at level 3-4 (plus flash) between the free boost, the move speed steal, and the innate burst that he has even without much AP. If he catches you with his slow under your tower, he throws in his stun and dashes to you. By this point, even without boots, he will sprint out of the other side only taking 1-2 turret hits. I do not quite understand why a champion needs two slows, one stun, a dash, and then even more chase power without building into it. Rest of the passive is fine, if extremely painful even early on (avoid his slow).
Q - Timewinder I like this skill. I have ideas concerning both directions:
1: I do not think that it should apply two passive stacks. 2: I think that it's initial damage should have a very minor increase.
This ability already is nearly impossible to avoid in team fights, as he is one of the few mages that wants to be in the middle of your team. This hands him either an execute, or simply massive damage, coming out of the gate on someone. That being said, a stun is also enroute, followed by a dash. It goes beyond assassinating carries to overwhelming them with no chance to escape. (This is, of course, not true in every situation.) That being said, it, by itself, as his only ranged harass tool, does very little. If you took the second passive stack away, increasing it's damage in the early levels very slightly, he could harass more efficiently, making up for the removal of his penalty-free tower diving ability.
W - Parallel Convergence Perfectly fine, I'd very very slightly reduce its area, as people are getting accustomed to casting it so you do not see the wind up.
E - Phase Dive This champion already has CC and a Get Out Of Death free card, I am not entirely certain why he needs a spammable avoidance ability as well. Granted that is not the root purpose of this skill, it grants him yet another method to suffer no penalties for getting caught. Despite this, I think the skill is perfect.
R - Chronobreak I honestly think that this skill's trail could move very slightly faster. Often I notice that players will utterly displace themselves due to the fact that they themselves tend to be moving rather fast by the end of the game. There again, the damage is still intense. You cannot simply avoid it because he's already been on top of you, dashes past your carries, and explodes his ult, wiping them from the map... and I say them because he will eradicate even tanks if they happened to be in his way. Speeding up the trail's movement as he himself speeds up would give him more precise control over where he will wind up, and who he is about to make disappear, while at the same time stop him from merely being able to flat remove himself from a bad initiation (only to initiate once again immediately as he just healed himself) and ripping everyone that was causing that bad situation 3/4 of the way dead for him to then mop up, without much hope of enemy reprisal as he likely just wound up well beyond chase range.
Overall he could use a few small buffs in certain gameplay aspects to enhance this very awesome role of Chronomancer, however a couple of things are blatantly broken, though I'm not sure how they should be fixed. These are just some quick ideas. Anyone else?