So usually I enjoy playing hard champions and mastering them. However, recently I haven't found any particularly good champions. Can anyone please help me out and tell me some hard champions to master that can scale in harder ranks? (Preferably Mid and Top but Sup, Jung and ADC are fine as well.)
Are generally harder to master than their peers
Malphite's pretty solid.
, highest skill floor in the game.
http://i.imgur.com/NzzBecC.jpg
Oh, you're talking about difficulty? Never mind then.
Vayne is hard to learn and harder to master. But once you learn her you can wreak pretty much anyone else.
Definitely hard to learn, but very rewarding. He can fight 1v5 at his turret get a pentakill and save the game. (When played exceptionally well and his opponents are stupid :) )
Anivia can be very rewarding to learn. She's not hard to LEARN but she's hard to PLAY. Learning how to build her correctly is ESSENTIAL and she has maaaaany different paths. Also deciding where you want to lane with her and what summoner spells you want to take makes her very customizable. You can go tanky with ROA in top, full AP with archangels in mid, or even take her support.
Gnar obviously. He has a fairly low skill floor but I've seen so many people (including me) play badly as him. His teamfight potential is insane but he really requires a cooperative team to do well. But that doesn't mean you can't succeed with him in soloq.
Irelia isn't super HARD to play but her skill ceiling is actually pretty high. It's easy to see the difference between an okay irelia and an amazing irelia.
Very low skill floor, very high skill cap. Like these guys. 
Learning these champions are not hard, but you have so much to learn when playing them. Mastering their mechanics is sure to benefit you.
Talon is the epitome of the balanced assassin. If you play him right you can easily assassinate and get out, but if you play him wrong you just get piled on and killed.
Orianna isn't hard to play, but learning how to utilize her ultimate in teamfights opens up doors for insane plays. Some people just wait for their enemies to forget her ball and then just ult as people walk over it. I personally kinda like to flash over walls with the ball on my head for a surprise annihilation. (this HARDLY EVER WORKS XD)
I'm not really sure here, but learning how to use your ult and when to place turrets and how to farm and how to easily 1v5 with zhonyas and which ult to use when and what build you want to go for and which lane you want to go in makes him an interesting champ to play. He isn't hard to play, but people that know how to donger will wreak you easily.
Rumble is hard, but his damage is high and he has an insane presence in teamfights. His laning is awkward and he isn't that great early game, but he definitely becomes a force to be reckoned with lategame (and once you learn him)
As much as I FUCKING HATE this champion, he does require some skill. However, lucky for all the people who hate to support, he is SO EASY TO USE. Yet some people are still terrible at him. Learning which target to grab, when to grab, HOW to grab, how to predict dashes flashes and walking and how to flashgrab is crucial. I hate blitzcrank and I refuse to play him, but he does require skill.
Leona requires skill because she's an initiator, if she goes in at the wrong time she can get her whole team killed.
Quinn is an excellent duelist. She is easy to play top lane but playing her mid or botlane IMO requires a lot more skill. In top you need to learn how to duel and cancel dashes and in bottom you need to know how to skirmish. In midlane she's more of a bad assassin. (never played her mid)
Ugh. Honestly there's hardly a single champion in the game that doesn't require some learning to do well with. Every champion can be perfected and every champion can be played well. (or badly) These are just the ones that came to mind for me.
I am really bad at Karma. I have no idea why. But she is VERY strong and benefits from knowing her mechanics. Knowing when to ult and which ult to use is crucial. She can be played top mid and support and each play style and build is very different.
Did you say hard champions?
ROCK SOLID
The champs sitting on lower popularity tends to be the guys that are hard to play since they are too situational to truly shine in most matches.
Top: 
Mid: 
(post nerfs, that is)
Jungle: 
ADC: 
Support: 
Nidalee, Shaco, Elise, Evelynn, Nocturne, and Lee Sin have some weird mechanics and are hard to master
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I can't speak for a lot of champions, but is a very difficult champion to master. Immobile mage with one form of hard CC (ult) that is facing dependent and on a long CD. She has the highest possible sustained dps output, but it is very difficult to position and land skill shots right to do it until you're used to her. VERY fun champion when you get rolling.
Azir. Powerful late, super weak early, wholly reliant on positioning and timing.
Yorick: every game you lock with him will be dodged.
. She is pretty hard, but her harass can be cray cray if u get gud with her.
Magikarp.
is very hard mechanically if you play him as an assassin (works top or jungle, and mid in some matchups), because you need to pull off perfect combos (like empowered-E>Q>Hydra>W>E>Q) in a very short amount of time (literally the time you spend between leaping and landing on your target) in order to assassinate somebody effectively. if you screw up your combo or miss your skill shots, you're usually as good as dead on assassin Rengar, but if you pull it off, you delete your target in a matter of 2 seconds. Bruiser Rengar doesn't need the same level of timing though because he just jumps in and starts flailing at everyone while his team follows up.
The other "hardest" champion in my opinion is... 
.
Nah, I'm kidding, really, I'd say because he requires a ton of micro managing competence, and late game he is immobile enough and his damage and positioning is telegraphed enough that you need to really have mastery of him to play against all but the worst coordinated of opponents.
is quite hard to learn as the difference between a decent bard and an amazing bard is very noticeable, you gotta know when to roam, when to ult, what to ult etc but he's rewarding once you know how to play as him
i consider him hard to play personally, Low skill floor but high skill ceiling, You have to know when to stealth, where to position yourself(more than most adcs) and if you can go in on a lone enemy.
He's really team-reliant, and I'd STRONGLY discourage picking him in low ELO SoloQ because of that.
You need to be able to understand her itemization, and she has an ABSURD number of build paths.
To play Dray-Dray well, you need to be able to make quick strategic decisions about whether or not catching your axe is worth it. Also, juggling is really tough to do effectively.
He's weird as all hell to play, with the way his soldiers affect his autos, and how hard it is to position said soldiers in the heat of the moment. Micromanagement is tough, dude.
Rage management is really important on this little cutie, because if you're kiting, you build up Rage REALLY fast and can accidentally go Mega.
Learning to consistently do her more advanced moves like the 7-ball ult and 2-ball on-the-fly stun take a metric shitload of practice
Good luck hitting your ult if the ball isn't on an engager.
No tips, how do you even play this guy?
Some of the best playmaking potential in the game, but effective use of his abilities is tough.
Her kit is extremely diverse and difficult to master, but if you can learn it, she's a terror to behold, especially as a support
Playing her is dangerous, you could break your nose while facerolling.
Azir, Syndra are pretty tough, and LB can be hard to master (SOMEONE EXPLAIN why Riot rates Cass as a 10/10 difficulty?)
Type support when shopping, everything that appears is hard cause they're so nurfed into the ground that their output levels are shit, if that isn't hard enough then build ashe ap.
is really hard to play right. Need the right items, know how to cs with his horrible AA's pre 6, and play it properly.
here is one for every lane
Lee Sin
You need to find someway to be useful.
