“He is very squishy and which makes it very easy for you to burst him down and get fed against him in lane. He's a good enough lategame champion though so he will eventually hurt.
Try to get fed from him, Roam and end the game as early as possible :)”
“I out-range him, so I just poke with E without going for passive procs and putting myself in a position to lose a trade. I'll build Zhonya's for his R, but there's no point rushing it as it doesn't deal that much damage early on. If he's some sort of god that lands every single Q, I'll get some Mercury's Treads. He's fairly immobile and pushes easily, so my jungler usually has no issue ganking him and slowing him down from scaling into a late game monster. I'll also spam ping when he's close to 6/gets 6, so my teammates are reminded to back or avoid fights if they're low on HP.”
“Hate him, ideally wait for ganks and all in him then. Otherwise experiment with the Karthus with a few Qs when you play against him. If you get a feel for how much damage you can do and how much you can take you will know when to kill him. Build Spirit Visage if scared and behind otherwise go normal build with Abyssal Scepter for more poke and damage.”
“very easy match up , you have everything to counter him , your w , your q to heal back his dmg , your w can block his ult , if possible , then try to avoid his w (slow) because if will reduce your movement speed and magic resist , but with that you can still kill him but its just a bit harder”
“Although he does do lots of damage, his skillshots are easy to dodge and he has no cc. I find this matchup quite easy as long as you can outthink the Karthus and dodge his Q spam. If he is rushing for level two, back up and respect it because the only real way to lose this lane is to take a terrible early trade from the level 2 disadvantage.You should be able to bully him early, and burst him out nearly instantly mid and late game. Buying magic resists is theoretically useful, but in almost all situations it is much better to have a Zhonyas to survive his passive or ultimate while also stacking armour for his allies.
“Karthus burns mana easily, and his Q wont do much damage early game, so just stop him from getting CS and hit your sleeps when you can.”
“Really easy. You can sustain against his poke, and his immobility makes it easy to land Rupture. One of the most useless champions once you land Feral Scream too.”
“he's pretty squishy and with how agile you are it'll be hard for him to hit a skillshot. dodge everything he throws on you and play aggressive. ”
“Start Doran + 2 Pots if 1) You think you can outplay her and hit your W's to generate a kill at levels 3-5 or 2) You think she will burst you down post 6 (get an extra ring).
Start Corrupting if you think you will not hit your W's (or you will get poked down) and you rely more on wave clear/spammy poke (you will be way more squisher but more durable -- this is recommended if you are sure you will not get hit by CC spells and instantly die).
Be careful of isolated Q (just like Kha'Zix). Play around minions and try to get a full combo on him. Remember if you kill him to back away as soon as possible because of his passive. Always keep in mind that he can ult when you are low hp or your team, so use pings to communicate. Ping when he makes level 6 so your team knows that an ult might come. Roam but keep in mind that if he has ult he will use it.
Try to go for the kill as often as possbile. Play with Ignite and get a stopwatch if you want to deny at least an ult.”
“Karthus comes as an extremely easy match up for Leblanc since he struggles to hit many abilities on her at all. Leblanc just has to hit full combo's and dodge all of Karthus' Q's and she straight up wins.”