This is for my friend Kotakumaro who need a new build for kathus.

This runes are for almost all mages whit a litle amount of life. The magic pen is for early game to more damage and also the ability power. The armor is FOR you NOT DIE.

This items are for life and ability power, nothing more. The rod of ages: AP, Life and Mana and generate more after every minit. You can sell the Dorans ring for other item you like.

Flash for escape, clarity to stay in lane. You can put another spell like exhaust and ignite are very good.

PROS

Very good late game; only kills

When you die you not die(passive)

Spends a little of mana but not whit 3rd power always active

Very fun to play

CONS

He is a little killstaler (is not a bad thing but can make your team hungry).

Low life

Early game is horrible whit him(Try to have a carry or suport in your lane)

Easy to gank, die very fast

Can be dominate whit spell shield or crowd control

Well is everything. Kartus is... you know. Go try him summoners!! But remember: KILLSTEAL!!!
NOTE: He cant farm well in early game.