Is a tematic build, like if you where becoming Kayle cause of the angelic theme of the items and the nashor's tooth with that attack speed.
Try to roam to help you team as much as you can, cause of the cdr and the mana you're not gonna have any trouble spaming E (you can also go top lane xD)

Karma is a flexible pick, almost the perfect champ: 50% winrate, low banrate, can go everyrole, have everything (cc, damage, heal, speed, root, shields, ap, uses the basic attacks) etc.
This can give a bunch of fun combinations.

There are a few combos that I love to do every game:
1) Q+E: just move around and throw dat laser beam of destruction, the moment karma moves her arms, click another direction and spam E. You're using the shield in the Q's cast, congratilations.
2) W+R+Q: imagine going straight Fiora, faint with the W (remember, don't go melee...now) she's gonna use that W, then you flash behind her and hit the R+Q. This move is also useful to finish a lot of champs, you might have low hp and they are gonna follow you, then you flash behind and burst them SHACO STYLE.
3) secrets of R+E: the shield do damage, yes, also that damage slows a little bit.
4) R+Q: you can cast mantra seconds before the minions arrive to low the cd before start fighting.
5) W+E: in laning phase (as supp) you can run around the minions landing basic attacks and then use the shield to receive no damage from them, then you can land W to poke while the Q can't go through the wave; also, you can use the same trick as Q+E

You have max cdr, you can go there spaming your E, they can't stop you cause you have mikael's and the talisman (and his passive); you can throw towers faster, you can reset mantra's cd so easy, you have enough defense so you're not gonna get bursted and if you do, you revive (you also have E, R+E or R+W to survive), you have so much mana and mana regen, help a lot your team and have damage.
This is the second build I share with the community (the first was a crit ratatoskr from smite, pretty good tho).
I hope you like it and give me some tips to try more fun, crafty or thematics builds.
http://imgur.com/a/Aylbm
Just in case, if you're playing againts Karma, try to not feed her, after all this is an "assassins meta"