Zilean, lost in time
It was all the way back in 5.4, Zileans Q was changed to a skill shot and given a stun. Seems like a totally legit change.
Except the targeting mechanic means you can't choose who you bomb, and the double bomb target radius is virtually impossible to land in any team fight scenario without existing cc. For a mid laner, he has nothing going for him. For a support, he brings some cool utility. But not nearly as much utility as any other support with more reliability. If you play nami, landing a q is an amazing feeling. Now land two of them, on the same target to get any effect whatsoever. And it requires two of your spells? Why such a steep cost for a champion who has nothing else going for him? His ultimate isn't exactly good. Planning for a teammates death is literally never applicable in meta, when you could have a champion who could _prevent _death. While it's a big denial to reset champs like Darius/Kat/Kha, it's almost useless in most scenarios where if an ap/adc is going to die, all the help in the world would likely not rescue them once they stand back up. If zilean's ult didn't have to go through the GA animation cycle, it would almost be redeemable.
The entire kit is simply clunky, and rewind is a mechanic that has never been fun or rewarding for the player or the opponent. Zilean simply needs to be built from the ground up, and giving him a better identity within his lore. Possibly keeping the Q as a single spell, and simply give him a new W and R. I wish some of the interesting mechanics that went into Ekko's planning were implemented in the time wizard that was thrown completely to the wayside.