[this is a work-in-progress guide]

PROS

+ It's fun
+ Lotsa sustain
+ Unkillable if you play correctly
+ You make people focus you instead of your carries thinking you'll die easy.
+ You can burn people's flash most of the times by running in trying to stun them.
+ You stun people up to 3.25 seconds while healing. That's broken af imo.

CONS

- Gameplay is slow af you might get bored if you're not into it.
- People might think you're trolling so they'll be tilted.
- You most likely won't get much help since people will think you're useless.
- You rely alot on your mana and it goes away rather quickly.

So basically, all you do in league of legends is farming for the first 10 to 15 minutes until people start to group.

EARLY GAME:

You farm. Don't die. If your enemy laner is an aggressive one, one trade will teach them not to mess with you. With Mantra you'll be able to heal using your Focused Resolve so that's a direct disengage tool in your kit.

Don't spam your abilities, remember your mana runs out quickly. If anything, try to use Inspire to activate klepto and get gold/items off of your enemy laner. Your main focus in lane should be using your klepto as much as you can while not missing any farm. This should be easy against melee champions.

Against ranged champions like Teemo or Kennen you should always position yourself in an angle around the minions so that they have to walk close enough within your Inner Flame's range to hit you. This way you should be able to hit them while making use of your klepto and allowing yourself to farm later on since they'll likely not try to touch you again.

In case you're getting ganked, your first choice must be always run away. If you're too pushed and your enemy laner is low on health and the enemy jungler is walking up behind you, don't be afraid to walk straight into the tower, activate Mantra and Focused Resolve to heal off whoever is closest to you while using Inspire's speed and shield to not get hit too much by the tower. This way you might get away burning the enemy jungler's flash as they try to catch you, and also your enemy laner's flash as they might think you're going all out trying to dive them.

If you ward and play safe, communicating with your team as to where the enemy jungler is, you'll never have to do this, but if you find yourself in this particular situation you must be ready to take this escape option. Sometimes it works better than running straight back to your tower accross the enemy jungler. You must mind what type of jungler they are and whether or not you can get away by stunning them. Otherwise you'll have to take the riskier escape.


MID GAME:

In the mid game, assuming your team's doing alright you could find yourself in 3 situations:


1. You're doing well. You've killed your enemy laner a few times now and you're ahead:

This might determine if the game's already won. Winning your lane with Karma using a tank build can heavily tilt your enemy laner. Chances are the enemy team might also be flaming and overall getting toxic due to your enemy top laner's poor performance to what they believed would otherwise be an easy lane against a Karma.

During this time you must have already finished either your Frozen Heart or Spirit Visage, so you can assist other lanes and group with your team. In this situation where you're doing well, your team will be more confident in following you should you want to dive people. This should be no problem with Inspire and Mantra + Focused Resolve.

Remember that your passive Gathering Fire reduces Mantra's cooldown. So while you activate Mantra and use Focused Resolve. For the 2 seconds duration of Focused Resolve you're already reducing Mantra's cooldown by at least 4 seconds. Added with a few auto attacks and Inner Flame, you've already reduced Mantra's cooldown a further 4 to 6 seconds, and that's only with one level in Mantra. Ontop of all that you got your 45% CDR from items and runes, so you should be able to dive, heal, shield yourself, take a couple hits while auto attacking and heal right back up again.

Under these circumstances you're the strongest you'll ever get to be in a match. Your main focus here must be to assist your team as much as possible, getting objectives and pushing lanes. You must NOT CHASE OR GET KILLS. You should end this match as soon as possible before the enemy team gets the chance to catch up. Communicate with your team and let them know that you must end the match promptly.


2. You haven't been able to get advantage of your enemy laner but you also haven't given them the advantage:

You're basically evenly matched. This is a problem. Being evenly matched means they're more likely to win a 1v1. If they can win a 1v1 chances are they're more useful in a teamfight than they'd otherwise be in the previously mentioned situation. This doesn't make you useless, however this means the match will be determined by teamfights rather than indiviual performance.

Your objective here is to be with your team. If you haven't yet shown to the enemy team that you're not as easy to kill as a Karma might seem then you got a pretty good chance to win the first teamfight. People don't usually look at what you're building, but even if they do take notice, in my experience, most people will still focus you at first thinking you'll still die easy regardless of your build. This is essential in your chances to win a teamfight.

Position yourself in the front line as any other tank would. Depending on your matchups, determine their type of engange and play accordingly, trying to bait them into starting the teamfight. Use Inner Flame to poke, let them know that your Q deals almost no damage, thus making them confident you're an easy target. Depending on their type of engange, try to keep within the range of their abilities so that they might jump or initiate the teamfight.

As a side note: Usually, you're not as impossing or otherwise have the better engange to initiate teamfights, your kit doesn't allow you for much in this situation where the teams are evenly matched. You should work together with the jungler (and tank support if possible) to bait a teamfight. Communication is key. If you find enemies out of position then you can engange, but if both teams are grouped then you must always try to make the enemy team initiate the teamfight.