How does one counter him as a squishy AD? Or any assassin for the matter (well, other assassins tend to actually DIE after a dive, at least). Since Mercurial's doesn't remove the debuff anymore, the only way I can think of is getting an unorthodox Hourglass (imagine Hourglass on Ashe, lol), and building as a bruiser on some ADC who can, which isn't all of them. Serious question though.
legionnaire991 votesUm dial a taric? O wait no more point and click stun
Um get a 
Need Gold 4 Tent1 votesYea, I play Kayle and I am aware she beats Zed (heck, don't need to ult ADC, just save ult for yourself and kill him). But blind pick you see :/
I even have to resort to taking exhaust when I mid as an ADC just in case. And for most part it doesn't help lategame.
WalkingInACircle1 votesYou don't. If you're playing Ashe, stay away from him.
Need Gold 4 Tent1 votesKinda hard when he has a threat zone of more than half a screen away. Not exactly Ashe but I'm having trouble with him as Kog. While Kog does scale off AP from hourglass, it's still kind of trash when you're playing as an ADC. (AP Kog loves it though, I know).
Sir Fuzzi1 votesYou might be better creating your own threat zone then. His ult only does gobs of damage if he's allowed to, so if he's taking mid then you might want someone like Quinn who can burst and control hard at short range. A defensive Fiddles might enjoy a decent lane too.
Honestly I didn't realize QSS didn't shake his ult. Does Cleanse not, either, then?
Need Gold 4 Tent1 votesCleanse never did, QSS got nerfed in this regard not too long ago. I want to main Kog, so I pretty much play him every opportunity I get, including top/mid/jungle. Level 6 now, but a lot of the games where I get S (not necessarily winning though), was due to the team actually looking after me. I'm finding it difficult to play this guy without team help, unlike Yi where I can Rambo and get away with it.