By Astrohawke18
I was missing an additional copy of Mirror Entity, Cone of Cold and Blizzard but replaced those 3 cards with 2 Haunted Creeper and a Faceless Manipulator and still managed to beat Heroic Sapphiron. I manage to last till we were both out of cards while I had the extra copies of Feugen/Stalagg for the win at. The Faceless Manipulator was not really required since the game lasted till the whole deck was drawn. Save your Fireballs for the 5/6 Necroknight as it helps kill Spectral Knight. I even wasted one Duplicate after stealing a Spectral Knight via Mirror Entity.
I really like the strategy of winning using Duplicate to get multiple Thaddius but I think a certain amount of luck is still required to get the correct draws and Sapphiron getting bad draws. This was the deck I used to clear and not with TommyJTheGamer's Warrior Deck. His Shaman deck for Kel'Thuzad requires a very good draw together with bad draw from Kel'Thuzad (Check out his YouTube video of the clear for an idea) so that might take a lot of tries too. I read people having success with Zoo Warlock so that might be something try clearing with. Edit: After writing this, I cleared Kel'Thuzad with TommyJTheGamer's Shaman deck and got the card back!