Karmic Justice is bugged, lets out get that out of the way. There is an error in it's coding that causes Karmic Justice to only calculate and be boosted by the Magic in your currently on RIGHT HAND at the time of detonation. What this means is that there will be no difference in damage if you're using Karmic Justice with Velka's Talisman (At 8 INT) or using it with a Darkmoon Talisman (At 40 faith) in your left-hand. So, if you want to use it, NEVER cast it on your left-hand.
BUT, this leads to a COMPLETELY unexpected phenomenon! Karmic Justice will take the magic adjustment of ANYTHING and make it the determining factor in its power when it is triggered. This means that, you can cast it, then switch -or hold at the time- to an item with a more powerful magic adjustment to increase its potential. This is the reason that this player was able to deal immense damage by using the TCC.
There is more. This spell doesn't just calculate magic adjustment, but also standard magic damage. Weapons, I'm talking weapons buff this miracle. Not fire or lightning, only magic. If a weapon has NATURAL magic damage, then Karmic Justice will treat that weapon's magic AR as spell adjustment, granted to a slightly lesser extent than how it treats real magic adjustment. Thankfully, this DOES NOT take into account magic buffs, but rather strictly the natural magic AR + whatever stat scaling boost you have. It also does not take in Magic Damage added by Moonlight Arrows.
For the sake to make sure this could not be abused (and should we be ready), I tested it with Dragon Stone Glitch and...IT DOES NOT WORK!