Hearthpwn

Update:

Since the strategy of the deck works perfect for Kel'Thuzad i tried it with other minions. With some it works pretty fine others took me a lot of attempts. You can find those minions at the bottom of this text with a Video for proof. If you have ideas about other minions i should try, just leave me a comment. Note: Trying other minions i put some more expansive spells inside the deck, since it is not always so easy as it is with Kel'Thuzad.

If you like the idea of the deck, please give me +1 ;)

Requirements:

- Have "Gang Up" until turn 2

- Don't have Kel'Thuzad in your Hand

Strategy: 

Kel'Thuzad is your only minion and will be summon on your opponents first turn. In round 2 use Gang Up with Kel'Thuzad and try to kill a minion. However, Kel'Thuzad must not die. On the next turn you will get another Kel'Thuzad. Try to kill as many minions as possible but don't lose both Kel'Thuzad. Next turn you get another one and so on. In the end your board is completely full with Kel Thuzads and you will win really soon. In the Mulligan search only for Gang Up and get rid of Kel'Thuzad if you get him. If you don't get Gang Up until turn 2 you can concede. So even if you have to start the game a few times, your fails won't take much time and in 15 minutes the Grim Guzzler is defeated ;)

Cards:

The rest of your cards have to be spells. Some spells make more sense than other ones. Fan of Knives is very good for the case that he summon the four minions with taunt. Blade Fury is good as well. I choose mainly cheap spells, to make the deck as cheap as possible. Especially if you try other legendaries it makes sence to use some of the more expansive spells like Preparation and Sabotage, but also for Kel'Thuzad those cards makes sence.

Threats:

• In some cases on his turn 2 he kills your first Kel'Thuzad with his remaining minions and the second one with Inner Rage and Execute. After that it is really hard to win. Preparation + Conceal on turn 2 after playing Gang Up prevent this. However, it is really unlikely that he can kill both.
  If he kills your Kel'Thuzad on the first turn with Inner Rage + Coin and Execute there is nothing you can do. But this is unlikely, too.
• On his turn 5 he often plays Brawl, which can leave you with an empty board. If you couldn't play a second Gang Up the game is over. However, your board should have more minions then his, so in most cases one Kel'Thuzad survives Brawl and summon the other ones again. Therefore it is necessary that he don't have the dwarf, which always wins Brawl. If he gets him on turn 5 you are just unlucky. Otherwise try to kill him as soon as possible.
• On turn 3 he plays sometimes the four 1/1 taunts, which prevents you from killing his minions. If he goes straight face he might kill you, before you can gain board control again. Fan of Knivesis an perfect answer. Blade Flurry is good as well and can be played on turn 3 with Preparation as well. If he gets a Stormwind Champion on the same turn, you have a serious problem ;)

 

You can see how it works in the following video:

You can use this strategy also with other minions. Not so successful, but fun anyway ;)  

Malygos gets you ridiculous Spell Damage ;) 

Ysera is a little harder, but it is working as well :D 

With Sylvanas Windrunner this deck is quite successful as well

I won't suggest that, since the win rate is terrible, but Majordomo Executus is working, too :)

Ragnaros the Firelord was easy as well

Chromaggus is doing an amazing job. Won 3 out of 4 games when i got Gang Up until turn 2. In the video i ended up with having 14 Chromaggus and could have actually fatigue him :)

It is not a 1-minion deck, but you can't split Stalagg and Feugen ;

I just crafted Baron Geddon and could immediately include him in this list

Foe Reaper 4000 is super effective.

First Rogue legendary i got: Anub'arak

First non-legendary: Force-Tank MAX

Sneed's Old Shredder is not very consistent, but the RNG makes it one of the funniest.

Adding Baron Rivendare to support Sneed's Old Shredder makes it a 2-minion deck, but the games can be even crazier.

Deathwing the king of the Dragons :)

Mekgineer Thermaplugg was a really surprise how good he works and it is fun to play.

Illidan Stormrage is a harder one

 Y'Shaarj, Rage Unbound is a pretty easy one

 Deathwing, Dragonlord is similar to Deathwing

 Finally, Blood of The Ancient One can be played and you can reliable get to see the ancient one.

 Faceless Behemoth is the second neutral that works. However, it is tough.