Singed and Heimerdinger.
You see, I'm sure these champions are balanced. However, they both have the same problem. They each force you to learn an entirely new playstyle specific to playing against them that you have no use for anywhere else in League. So the fact that I encounter these champions once a month or less in lane, means it's literally impossible for me to learn how to beat them.
Singed: -The only champion who clears waves behind your turret, removing your minions without you being able to chase -The only champion who deals tons of damage without the need to engage in any normal sense -The only champion who you can't chase even if he is 200 hp, he'll have 600-900 movespeed and tons of health regeneration, so if you want to actually kill him your only option is pre-6 (before he can outrun every champion in the game)
Heimerdinger: -The only champion who has high damage zones you can't enter in lane -The only champion who you can't kill solo because of his death zones unless he does, in which case he's bad -The only champion who can kill you in 2-3 seconds while using stopwatch/zhonyas -Probably the lowest effort champion in League of Legends
The problem here is that these champions are so rare and have such playstyles to where you either lose or win not depending on your skill, it really just depends on their skill. If they are stupid then you win if they are decent then you lose. You can't do much of anything to outplay Heim since he just needs to walk and use W/E and if he's bad at that then he's really just bad at video games. Same with Singed, if you suck at running away than you need to re-evaluate your life choices. Their unique playstyle (is it easy to agree that they are the biggest outlier champions in league?) forces you to have learned a completely separate playstyle just to know how to beat them. This is completely unfair because the less these champions are played, the higher their win rate. This doesn't apply as hard on most champions because their playstyles are remotely similar in that you have to go to lane and you have to hit your abilities and position well. Except for those 2 for some reason.
The fact that these 2 aren't scheduled for a rework just makes me confused at Riot's goals. Why rework somebody like Irelia (who is a pretty normal champion with normal abilities and normal playstyles and a real learning curve) when you have these champions that just ignore the basic rules of a game like this and just walk to kill? How is it balanced to have champions with literally no skill and to beat them you actually just have to do nothing for 20 minutes and hope you get ganks. I mean, Riot seems to care about healthy mechanics and agression over passive games so...fix them? Do anything with them? Make them moderately normal? If you can't get them to be normal then at least make them on the same level as Shaco?
*Shaco, Olaf, and Nunu are minor versions of this
Side note: I regret a lot of posts I make on the boards, but this is something I've been thinking about for years so I'm going to stick to it since I passionately believe in everything I'm saying here but I suck with words so I'll try to give as many explanations as possible, not just blind rants.