Hey man! I' m not a kata user but i gues si can help you in few things
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Against a mid you will suffer terrible terrible poke, mostly magical. This leaves you vulnerable and in need of some form of tankyness, but sadly there ar enot many magic res options for katarina ( besides that void staff), and since health in lane phase is not a good bet you are left with spellvamp.
Take guinsoo if you are snowballing, since she has mild ad scaling and the active is good, but overall prefer will of the ancients since it' s cheaper and gives so much needed CDR.
-
Fopr boots always prefer sorcerers or lucidity, since che is an assassin she needs to kill, and take lucidity only if you are planning few cdr. and you should not do that.
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Sheen and lich bane are your friends! they add so much needed burst power and mobility to you, allowing you to get better objectives and change better duels!
Also deathfire grasp
is really useful form execution and cdr, but it' s gonna be removed soon. don' t get too much attached to it!
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At this point you might consider zhonya, since it allows you to escape endangered situations with shumpo, retreat after a failed ultimate or cast it by surprise. get
before if the enemy phisicals annoy you
-
do not get rilay or abyssal, the first does not help you very much ( you survive mostly by skill ) and the second is better taken by another one. If you feel squishy take guardian angel instead, or void but only if there are other magic dealers in team that does not pick it.
6)now, once you got AT LEAST 2 AP items you can get the crown of death, the
! you coudl get it earlier if you manage to buy a
earlier, however.
- void is necessary, but only after 2-3 enemies got mr AND only after rabadon. your base damage is lackluster!
i checked some random guides and follow up more or less what i said. the best thing i can say however is listen to me, try yourself and make your own idea ;D