No, this isn't a troll guide. This is legitimate and has been used in ranked when played correctly. Full credit for this goes to Dumbledore Mid on OCE who talked about this on the Karma mains subreddit.

Your goal is to get max CDR as quickly as possible; this means not always finishing items over getting another Fiendish Codex for that final 10%. Ultimate Hunter/Cosmic Insight/Cloud Drakes can further empower this playstyle. While it may feel a bit strange, the faster you hit that 45% mark, the more impact you'll have with Mantra.

Karma is a great annoyance in lane, as even breaking even means that the enemy isn't coming out far ahead in farm/kills, and Hail of Blades makes her that much more dangerous. Great matchups are ones where either the enemy has low mobility, or is melee and has to engage.

This build would classify Karma as a battlemage. Karma thrives in drawn out engages and teamfights that give her the chance to constantly refresh Mantra.

Let's look at some statistics for a minute.

Hypothetically, let's say that you're at 45% CDR by level 11. No Ultimate Hunter stacks besides the one you automatically get, and no cloud drakes.

This means Mantra is on a 20 seconds cooldwon, and Gathering Fire is currently 3 seconds for abilities/1.5 for basic attacks.

A basic spell combo without basic attacks will reduce Mantra's cooldown by 12 seconds, with an additional 3.5 seconds as it takes that long for RQ/W root to activate. So from 20 seconds, we are already 3/4 of the cooldown away from refreshing it.

Now add Hail of Blades, three super fast basic attacks, each one granting 1.5 seconds, equaling another 4.5 seconds.

A properly executed RQ/W/HoB combo now instantly refreshes Mantra And with Q on a 2.75 sec cooldown with 45% CDR, this means against a solitary opponent you could open with RQ, and end with another RQ.

Now add one or two Cloud Drakes, and a few assists, and Ultimate Hunter will bring your ultimate down to around 13-16 seconds. Every teamfight can essentially begin with a RQ, and if you hit 1-2 enemies, RE will be available moments later. Her teamfight potential becomes even stronger, as she's not just a shieldbot in the late game; sho's also consistently throwing out huge nukes. Couple that with Morello/Liandry, and you are making an enormous impact on the game.

In lane, look for abilities that you can initiate on. The minute an enemy misses a key ability on you, engage with either E or RQ, and follow up with RW/Hail of Blade attacks. Unless there's no chance of them counterattacking, save your early Mantras for RW as the cooldown on Mantra is still quite high.

If the enemy has strong all-in potential, focus on poking/pushing the lane. Enemies like Zed/Leblanc/Velkoz have to use their abilities to farm effectively, giving you opportunities to harass them. If the enemy has strong wave clear, let them push up to your tower and coordinate with your jungler to gank them. Even if its just to burn their flash, that gives Karma the ability to be even more of a pain going forward.

By the mid-game you should have Lucidity Boots/Fiendish Codex/Lost Chapter, and from there finish your Lost Chapter Item. Now you're at full 45% CDR, and hopefully you've had a few assists/kills so you're at 3/5 Ultimate Hunter stacks. This brings you to roughly 13-16 seconds Mantras, meaning a good spell rotation will automatically refresh Mantra.

Start looking to roam with your jungler for ganks/objectives, and get Zhonyas next. Those few seconds of stasis could be just enough to get off another RQ/RW/RE depending on the situation.

You should have either Liandry/Morello at the very least depending on the enemy team. If they have Soraka/Sylas/Vlad Morellonomicon is the way to go. It's Zac/Ornn/Mundo go for Liandry/Rabadon

Almost every teamfight should begin with an RQ. If the enemies are grouped up, this could refresh Mantra on its own, and then you can RE your team. If there is a slippery assassin going for your ADC, try using RW on them. Since you've maxed it second, a successful RW is the longest root in the game, and almost guarantees their death in the late game.

You still want to focus on shielding/peeling for your team in the late game, but your build guarantees far more Mantra casts in teamfights.

Let me know if you have any questions!