if you have half hp in a lane vs lb.

{quoted}

teach me how to bea tleblanc. give me 1 tip that works for all champions vs leblanc.

She has a lot of weaknesses - her dash is interruptable, preventing all damage. Her damage is dependant on performing a combo - if you break the combo with disables or banshee, it plummets her dmg. If you get a kill on her in lane, she becomes near worthless all game. She has negative HP, and dies from a single disable in a teamfight. She has no sustain, so any damage you do to her sticks. The nature of her kit having zero sustained damage means if she can't burst you in one go, she plummets in effectiveness. A banshee on your ADC totally wrecks her late game potential. She is literally a one-trick pony. If she can't oneshot the adc, she dies instantly, and the adc will just lifesteal it all back in five seconds.

If you look back on all the so-called OP champs that were nerfed, she is really tame - she's not even that powerful of a champion in terms of securing the win - she's just good at killing champs and hoping the rest of the team can secure objectives. No matter how fed LeBlanc gets, if her team sucks, she can't win.

If you want a legitimately OP champion from recent history - post-remake Mid AP Evelynn with DFG, chunking entire teams for over 10k combined damage from stealth, with no chance to retaliate or prevent it from happening. She could 1-shot you from stealth faster than LeBlanc, and with even less recourse. This is a champion who was OP because of her teamfight potential -in addition- to her oneshotting champions. This means if Evelynn ever got fed, and she did almost every game due to her unparallelled ganking potential, the game was automatically over, because now your team had zero chance in teamfights due to Eve being able to build tanky and not having to rely on killing the enemy in a single combo, AND you couldn't rely on split pushing since Eve can show up any any moment and blow you up. LeBlanc really struggles in teamfights, and even if she's 29/0/20, she can still die at any moment from a single mistake, and lose the entire game in a split second. Most other champs if they're fed that hard are able to take some punishment, but if LB builds tanky at all, she loses her ability to oneshot and then she is useless.

And beyond all this, she can just be beaten in champ select. AD champions naturally have an advantage since they usually get scaling MR, access to hexdrinker, and can build Lifesteal to counter her in lane. She is countered by champions with any combination of high mobility, reliable poke, high burst potential, point and click or instant disables, high wave clear, sustain, shields, and general tankiness. Cho and Lulu are her hardest lane counters, but many others have a lot of tools to deal with her. It just takes quick thinking and maybe some jungler presence, but that's the same for any champion.

She's really not difficult to beat - especially right now, she's weaker than she's ever been, and she used to be considered flat-out terrible, and a troll pick, even with silence and higher AP Ratios. People dealt with her for years, and she's only become easier and easier to fight back.