That is the question.
So this is just a little blog I will be updating about my progress with karthus. He is top tier. He is loved by many and hated by many. This little blog will cover what I have learned from him and how I feel it is best to play him.
SO over extending....
Well I find this one quite a weird issue with karthus' as of late. I see a few who like to jump into the frey and hope to pick up kills while people are standing on top of them. I think it is hilarious when they flash into group get focused then the group backs up... So here is what I have to say about that. It is silly you should never try to kill people with you passive. You should try to kill people out of position... Here is how you should do it. In solo 1v1 you poke with Q and after you have the advantage you throw down your wall. I like to lead them with my q and take off a bit of damage but not to over commit if they have to leave the lane you can get 6-10 minions up on them by the time the come back. How much is that? a whole kill. You shouldn't ever really take turret aggro early game 1v1 with karthus. Don't trade, it is not worth it. You are hurting your team by being dead and if you fail it is wasted. So don't over extend, push them back to they have to recall and occasionally you will get a kill because they didn't have the right runes or right champ to lane against you. Just win you lane in gold not kills and not in turret. Minions are more important with karthus. You can pick up kills from escape flashers who almost got away the whole game. So don't bother turret diving.
When to engage? OK you should be at the back of the fight dude. Don't poke with your q... they have range too and if they focus you or cc then your whole team loses because of you. All they have to do is get 1 slow or stun off on you and then they focus you down back up wait a few seconds and reengage and win. You are at the back. Tank in front. When they come in for him you throw down your wall, and lay waste once the time is right and they can't move to attack you you pull up your E and do massive aoe. Not until they are already engaged. You need to be at the backish if its 5v5. When numbers start dropping move up and then use your wall to cut off retreat.
This is how I play him as far as engaging. I really dislike how karthus' like to trade and then lose the game for teams while they are dead. 4v5 is game losing a lot of the time. So if you are gonna play him focus more on your minions. I go 300 minions a game with him and i would take a 6-3 KD over 10-8 any day. Just think how many times have you lost a game because your main dps is waiting to re-spawn....