Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
I have been using Karthas for awhile now, and I can tell you that he is the ultimate dominator for Kills and Team Assists. This guide is to help your team win every single team fight no matter the skill level if you do this right. My record is normaly 4:1 KD. The average game I got 12/5/15.
When you get archangels staff by level 7, Make sure you are spamming Q button and using Clarity when you can, to keep increasing your mana pool. This in return adds to your AP later on.
Always Use teleport to get back into minion kills or protect a tower. NEVER worry about ganking, no matter how much your team needs you early game...your to weak. Only help mid-late game.
Always try to take mid. This is the key to building Karthas fast and getting fast kills early. WHen your mid, never ever ever worry about killing your enemy champion. Greed is failure with Karthas. You can Occationaly Toss a Q at the champion to keep them on their toes. Just keep Last hitting with Q and build your bank up asap. Save up 1100 Gold before returning if possible to get Sorc Shoes. Then Tele back asap to keep grinding on minions. Again, Do not worry about killing early untill level 6.
At level 6, is when you really start shining. R is going to be your priority killer untill level 13. So while laning, The trick while killing minions, ALWAYS be looking at your mini map. If you see battles happening in any lane, Check the enemy's life. At 6, you should be able to kill with 270 life left. Run back to your turret then Kill the enemy. Keep doing that untill level 13. ALWAYS checking to see for low health users. This is where most people fail early. They do not watch constantly the enemies life.
Now that your are 10, You should be pushing minions and not going for ganks or kills. Keep farming gold as much as possible, your major damage comes in late game and where you shine as team support. By 10, you should be around 3/1/2 stats. Sometimes you will get ganked by folks not calling MIA. Thats ok...just dont die alot. If lane phase ends before level 13, do your best to keep farming jungle racking up money, you need your items for late game.
Now your at least level 16 and ready to win every team fight. Now here are they major keys to winning team fights every time:
1) NEVER RUSH IN, you are last to go in always.
2) Always have an ELIXIR OF BRILLIANCE ready to be popped for team fights.
3) Always make sure your tank tells you when they are going in.
Now here is the secret...Use your Ult as the tank goes in. THats right, Most people wait till the end of the fight to get the kills....WRONG! Use it at the start. Here is why:
When you use it at the start, You should be doing around 800-1200 dmg instantly. Now they are at a disadvantage with half life. As your team is wrecking their life, You walk in with Defile up (E), taking their life away fast. WHen your in the middle of it all, Pop your zhonyas ring and start mashing Q at every enemy. You should get about 1-2 kills and 2-3 assists after all is done. After 3-4 teams fights doing this, They will surrender, trust me, they always do.
Just be patient early game, Do not worry about getting first blood, and just focus on your money and last hitting. By end game here are my stats usually:
Ult hits for 1200 damage
15 Kills 5 deaths 18 Assists <---My last game
( I also do not get Wall of Pain untill level 8, because you will be Mid and wont really use it much)
Follow this guide and you should be fine. I have yet to have more deaths than kills with Karthas following this build.