leblanc is one of the most powerful champs in league lorewise. Leblanc isn't even leblanc, she's an illusion of the real leblanc so powerful that it could enter league on its own.
imagine this,
leblanc passive - leblanc can pick a teammate like kindred's passive pick's enemies. If she's standing near somewhere the enemy can't see she may randomly spawn an imitation of said champ. She can also do herself. If she drops below 30% she stealths and 4 blinky spots appear around her. She can click one to escape or make a play or somethin but then they all go away.
Q - mark a champ for a really long time with a skillshot. If you can land one of these for each 400 hp they have on this champ before they go actively get rid of it they just die. No matter what kind of defense they have boom dead. Increase the range and decrease the damage though. Deals aoe damage around the target like a Taliyah Q and marks all targets. When a champion or minion dies maybe it should spread the marks around like a bloody circus act.
FO MUH NEXT TRICK!
W - deals more damage to marked targets and has bonus effects if they have so many marks. Deals very little damage, unless you are marked, but the cooldown should be lower.. like urf lower. Leblink all day. What is mana even. No mana cost. Redistribute mana costs.
E - if the chain completes they get double marks. Should cost a shit ton of mana and have a long cooldown. This will often be the big finale
R - same as before. Cooldown should match that of E with its increased cooldown.
Traditionally I think this is what the most healthy assassins would look like. There are also other types of course but a lot of those aren't very fun for both sides and wouldn't fit well into league.
But then they also have other things different...
for example. If she were a more traditional tank.
Increase all cooldowns.. like seriously just double them. Everytime someone triggers her passive it should take a second off the cooldowns.
Passive - Lasts 1 second, is no longer consumed by activation. Reduced cooldowns when triggered.
Q - Same as before, but slamjam levels of damage if the target was already slowed or had some other CC. Remove buffs against a target, cooldown reduced against targets with sunlight.
W - Same as before but now gives her slow resistance and tenacity while its up. No explosion just burns everything around her slowly like sunfire. In fact give her a tiny sunfire effect that causes her to draw agro under towers. Procs her passive while active ability is in play.
E - same as before but with higher cooldowns, cooldown reduced against targets with sunlight.
R - The beam of light stays there and continues to stun and slow in the same zones for like 2 seconds. This ability no longer has a cooldown. She can only unlock it by charging it up by having her passive proc'd
**Keep in mind this is just a glimpse at what the more traditional looking setup would be. Tanks normally aren't viable as damage dealers but do have brief moments of slamjam, especially at early levels. Assassins usually have something that nobody without a special defensive ability is going to survive if they just sit there and take it. Tanks will need a few extra passes but wont be given the chance to run either. Rangers should be kiting that much harder and should all have unique aa abilities to make this work out. **
**But league is league, these aren't necessarily the most fun setups, just what would make things work the way riot probably wished they could and balance itself out. **