Thresh Bug
I just lost a game because of this glitch - which I've seen in nearly every single game with a Thresh in it since Thresh was released. I'm genuinely surprised that you guys haven't fixed it, removed it, or balanced Thresh around it.
Setup - I'm playing Cassiopeia running away from Thresh and Azir, I'm close enough that I see Thresh throw his lantern to catch Azir before he disappears into the Fog. I immediately turn around and get ready to go ham on them both. As soon as I see the bubble for Azir appear, I drop my ult. I hit both Thresh and Azir with the stun, and immediately cast my W. As soon as my W goes out, I see Thresh's hook attach to me. Note that there was no visible windup, there was no animation, I was just... hooked. So now, I've got Azir and Thresh stunned and unable to move and I should be able to devastate them, except I'm stunned as well. The stun on Azir and Thresh wear off before the Hook stun wears off, and suddenly despite the amazing setup, I'm on the losing end.
As I said, this is a glitch that I have seen... basically every single day for more than 3 years. There is a really easy fix - clean up the hook so that the delay is a cast time rather than an arbitrary waiting period - and I would strongly suggest that you make the hook break if Thresh is hard CC'd, both to make Thresh mechanically interesting to play against (he's not, mechanically he's exceedingly toxic to play against because he doesn't really have any counterplay other than being bigger and tankier... which is not counterplay,) and to absolutely quash the chance that bugs like this happen in the future.