Nidalee

ff, turns game into cancer u really dont want that as karthus

Bel'Veth

really unplayable, cant hit a q ever on this champ and her e literally nullifies your ult. She has several cheese invade paths which u can do very little about. Can raptors into your gromp while ur on it and give cancer. Can also start on your raptors and split the map. against a good belveth u are almost garunteed to skirmish early game. If belveth is good in the meta this is a decent ban

Kayn

imo one of the worst matchups u can get as karthus. Its belveth matchup pretty much but weaker early. has 2 invade paths can raptors to your gromp or start your raptors and split map. You dont want any of those things to happen so ward his raptors vs kayn so u can anticipate what u need to do depending on his option. Once he gets form u are completely useless vs blue kayn. he one shots u and can take over game. If he goes red its chill the game is winnable

Hecarim

this matchup is kinda rough bc u can't rly 1v1 the hec unless hes behind by a lot. Whoever gets ahead usually wins this matchup. U could possibly take exhaust vs hec, hec gets rly ****ed from exh. Hes too fast so its hard to land a Q and if hes fed expect all your camps to be gone perma and to get one shot.

Diana

hard if she gets ahead, u cant rly 1v1 this champ at all when even and especially if she goes tank diana. Clears fast and high tempo just like u.

Brand

this champ is a copy of you. Just hard to throw q's on this guy because if u even walk close to him u get stunned by his combo and 1 shot. He has better obj control too.

Elise

nidalee but more playable. If she dosent completely take over the game its free

Graves

skill matchup, cant rly 1v1 this champ ever tho

Kindred

this is my permaban, you really need your mid to bail you out of this matchup and get you prio, if your mid is gapped then its prob ff 15. you can't 1v1 a kindred ever past 1 item even if you are way ahead, it is very hard to land Q's while she has her W active which gives her movespeed and also she can use her Q to dodge one of your Q's and it resets cd very fast which makes it rly hard to skirmish against her lvl 6+.

Rengar

really aids matchup, u get infinitely one shot and cant fight at all

Udyr

XDDDDDDDDDDDDDDDDDDDD? ?D? X?D?D D? D ?D?XD?D
u do no damage to him at all and he runs you over, this is possibly the worst thing u can play against as karthus besides nid

Viego

kinda hard to 1v1 him if ur not ahead, he beats u if even and hard to land a q on him. this champ also spawns in with like 5 kills randomly some games its not fun to play vs

Ivern

Master Yi

watch out for lvl 2 invade, his w cancels your ult

Lee Sin

awful matchup, u cant 1v1 ever no matter how fed u are. He controls the map and can invade, has obj control and good ganks. this matchup way harder in high elo tho compared to low

Lillia

this champ is pretty much same as hec. too fast, cant land q on her and her R makes it hard to play vs in teamfights

Talon

jg and mid role this is annoying to play against. u cant 1v1 this guy unless ur really ahead and he one shots. feels like rengar

Karthus

every other champ is fine for karthus. Karthus is a champ where matchups dont matter too much, ur just playing to farm and press R in fights and do a lot of damage. The only matchups that are really troubling are lee sin nid and belveth kayn. Those 4 champs can completely control the game and do things early to ruin the game for you. The other champs can't do that and its just bad 1v1 situation but you play your role as the main ap damage dealer for time and control objectives.