This is my take on Karrthus EDH, I've had this deck for a long time and have fine-tuned it into the monster that it is.
First off, why Karrthus?
The purpose of this deck is to make a Dragon tribal deck that can pump out constant threats and bring late game inevitability. Karrthus is in the right colours for this, with RGB his colours include the strongest dragons. Karrthus also does not bring the same threat level as Scion of the Ur-Dragon (who can one shot a player with a single swing of the commander). At 7 mana, 3 colours and haste he is much easier to cast compared to The Ur-Dragon. Overall, Karrthus is a powerful option for a Dragon tribal deck.
Notes off of this build:
My build of Karrthus is much more about support and mana ramp than a typical dragon deck, so it's not loaded with as many dragons as one might expect of someone touting it as a "Dragon tribal" deck. I've taken the most powerful, most devastating dragons and build a deck to power them out.
This deck has been around many different meta's and is mostly fined tuned in a meta where there are not a large number of counterspells and no turn 3-4 killing decks like infect. Some of the cards in this deck can be swapped to fine tune for your meta if early game aggression is a problem, swap for lower cost board clears and more instant speed creature removal. Against counterspell heavy games, you much need to swap in Vexing Shusher and Prowling Serpopard. That being said against counterspells, this deck is pretty resilient, more about that later.
Dragon package:
The specific dragons chosen for this build are all bombs to land and to anyone who has angered you they present a serious threat. Sometimes, simply casting Karrthus, Tyrant of Jund after a player has angered you is enough, a 7/7 flying haste is a 3 turn clock from commander damage. If he gets wiped away from a board wipe, he has haste so swing him in again if needed!
As to how to use or tutor for these dragons, it's pretty self explainatory. if you have Sarkhan's Triumph and you don't know what to grab, when in doubt, get Savage Ventmaw, need to kill creatures? Go grab Deathbringer Regent.
Non-dragons:
Some creatures are just too good to leave out Elvish Piper can get you there when you're mana tight, or simply offer you a huge discount. Avenger of Zendikar and Oracle of Mul Daya need no explaination. Drumhunter is on the weaker side but it's ramp+card draw, which makes it good enough to put in! Archetype of Endurance ensures nothing of yours will be targeted, and opens up your opponents creatures, it's mainly in here for Defense of the Heart however, more on that later.
Planeswalkers:
Liliana Vess and Vrasha the unseen are slightly expensive tutor and removal. You cast then and use their -2/3 the turn you play the, if they survive well you're about to get more value, and if not then they absorbed some damage to your face.
Ugin, the Spirit Dragon truly a house, typically you play him and minus him in the same turn.
Notable other cards:
Selvala's Stampede a must have, generates incredible value or mana efficiency.
Zendikar Resurgent Mana Reflection create unbelievable amounts of mana and let us close out the game.
Defense of the Heart a tricky card to play and requires politics, you usually want to slam this turn 4 and say "alright guys, lets calm down on the creatures" and play it off as a calming effect. When people get concered simply say "just keep your creatures low and nothing happens". It always triggers. Someone will trigger it, someone always does. It might take a few turns for people to forget and play into it but in the end it happens.
This card is also why we run archtype of endurance despite it being a good card in itself. More often than not I've cracked defense to go grab some high powered dragons only to have one player remove one immediately or both of them, thats why Almost always the 2 cards I get is Archetype of Endurance + Utvara Hellkite
, but regardless of which dragon I decided to get arhetype is always paired in the search.
How to win/end the game:
So this deck comes with build in inevitability in the form of Diabolic Revelation, once you've got enough mana you can dump it all to grab cards to close everything out, sometimes if the board is worry some, you should spent all but a single reg mana and search out then cast Blasphemous Act.
What to grab, this deck comes with 4 cards made with the purpose of closing out the game Genesis Wave, Dragonstorm Rise of the Dark Realms and Praetor's Counsel with Dragonstorm being the weakest and typically the least included in the search. you also can grab either Mana Reflection/Zendikar Resurgent to spice things up.
How to play it, really, it depends much pressure is put on you after you resolve Diabolic Revelation but the play usually goes like this, play a mana doubler and cast a subpar but still good genesis wave. Sometimes you can cast both the mana doublers and pass for an all out genesis wave next turn, but that is super greedy. The expectation is that either there is a board wipe to kill the now threatening board you have, or you beat them to death. If there is a board wipe, rise of the dark realms time. Same expectation here, board wipe or death. to finish it all of, if they are somehow not dead by this point, play Praetor's Counsel, bring everything back into your hand and go again. I have yet to ever had a game where I resolved a Genesis Wave and then Praetor's Counsel and didn't win.
