Mejai is a staple on kass, if you can build some stacks early, which isnt that hard since he has such great nuking/ganking potential + escapes he can snowball really fast and almost 2 shot squishies.
I'm using mpen reds, mana seals, ap per lvl glyphs, and current 1 move speed quint(i plan to get more but i need IP for leblanc) and 2 hp quints for some extra hp early on.
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For blues, CDs or APs are fine, and for Quints I honestly recommend MS/AP. MS are great seeing as he has a built-in blink that extra speed is fine. AP flat isn't bad either.
I take heal and ignite. Yes, heal. It's saved my ass countless times, and it's the ultimate baiting spell. Ignite is for early game, but if needed you can exchange that for teleport/cleanse/w.e you need.