The main Champion that needs to be updated in the Assassin Update
I remember reading things where Riot said they want to fix Rengar and I think Akali in the assassin update, but they haven't seem to have mentioned the champion who needs it the most; Fizz.
Not only his he not fun to play against, but both his passive and W seem useless when it comes to killing people. People only use the W for the damage over time to finish people off and not for the powered up autos and his passive doesn't work with the rest of his kit.
With the mage update, while they did show a lot of love to all the other champions like they did with the Juggernaut and Marksmen reworks, it does seem like it's mostly about Malz. So if they do a similar thing with the Assassin rework, maybe they should have a good amount of the focus on making Fizz better designed and not as annoying to face.

may be hated by a lot of people, but shes actually one of the healthier assassins. the problem she has is, that if she fails to assassinate her target, shunpo doesnt reset and she has no way back out. this is what i mean by assassination attempts to require commitment. if they fail, it should leave the assassin in a vulnerable spot.
isnt as bad as leblanc. his only design problem is that his troll pole does way too much for one ability. if you look at the rest of his kit, hes actually a very healthy assassin. a lot of his assassination potential relies on him hitting a skillshot with his ult to amplify the damage on his abilities.
is another example of a generally healthy assassin. with his only issue being that waveclearing and poking from a distance is too easy on him. which makes him kindof a lane bully. imo they just need to put more of his waveclear potential in his e, since its melee range. means he has a harder time to stay back and poke/cs with his q.