Balance Suggestions
There has been a lot of talk about champions that need to be nerfed right now, but I've seen very little talk about the ones that need to be buffed. The rylais changes hit several champions extremely hard but I haven't seen any real followup for them besides Taliyah. Since it's the holidays, no Rioters are probably going to read this but whatever.
Vladimir: He is currently one of the worst champions in the game for every single role. The Rylais nerf sunk his already low winrate into the gutter. I believe that his healing is fine, so my suggestions are to improve his sticking power by either reducing the self-slow on his E or by increasing the length of the enemy slow on his E. After that, a tiny damage buff basically anywhere on his kit.
Fiddlesticks: His mediocre winrate is misleading, almost everyone who plays Fiddlesticks is a hardcore Fiddlesticks main. When that's factored into account his winrate in every role he's played in is atrocious. My suggestion is to make him feel less clunky by making it so that whenever a target being drained by Fiddlesticks dies, the drain passes on to the next closest target. His fear pushing people away is bad because every other part of his kit wants to be close to his enemies, so I would special case the fear overhaul for Fiddlesticks by classifying his as a "Terrify" and make it so enemies feared enemies try to move around Fiddlesticks in a circle.
Cho'Gath: This is a hard one because he's had so many buffs before but he keeps on falling into really crappy winrates. Since he was a big Rylai's user that got hit hard by the nerf, I'd recommend buffing his base move speed and either his mana costs or mana regeneration to increase his sticking power. Buffing his Q and W cooldowns would also be a good idea.
Heimerdinger: He's in a similar situation to Fiddlesticks because his winrate is comparatively very low for how hardcore his mains are. I would actually recommend a Shyvana-tier for Heimerdinger, his passive is extremely useless and unnoticeable right now. I don't know what it could be changed to, but I think Riot can think of something that will bring his kit together and take him out of cheese pick territory.
Tahm Kench: The suggestion I wanted to put here was actually already posted on these forums. Make his passive and W work on blue and red buff. I recommend extending his passive to all monsters, since the jungling changes hit him hard. I'd also say to buff his early defenses so he feels like he can hold his own earlier in the game.
Ivern: Don't pull a Sejuani. When you inevitably nerf Redemption, please revert some of the earlier nerfs to him. Redemption is a huge powerspike for him and having it nerfed along with the nerfs that he got because he was strong with redemption would throw him in the gutter for no reason. That'd be really sad since he's the only competitively viable support jungler right now.
Nidalee: When you buff her, please don't make the same mistake as last time and give her absolutely insane clear speed. I've almost never played her so I don't have any other suggestions.