Karrthus is also my Main Deck, though I built it around only a handful of Dragons. It plays 16 Dragons only and relies on extra combat phases, though can also produce a massive army to overrun you or kill you off with the Wrathful Red Dragon + Blasphemous Act (or Chain Reaction) Combo. If you fight against Dragon Decks, it will be easier as well, thanks to Karrthus' own amazing effect :D - No good stuff Dragons in my (no Old Gnawbone, or Ancients!), No expansive staples... quite Budget with less than 200 bucks in value ^^
It's a little bit of a glass cannon (at my build is), but God damn do I love my Karrthus deck. Ur-dragon seems to be a pretty common dragon commander, so playing Karrthus against them is insanely fun. What makes it even better is when your opponent has no idea what Karrthus does. Seeing the look on his or her face when you steal his or her entire army is absolutely priceless.😂