Hearthpwn

I've tested this deck and used it five times, and I won four times out of five. I've tried using Deathrattle minions to make it hectic for Sapphiron, but there wasn't too many viable ones available. Considering how they don't get an attack in unless they have Charge, they are next to useless in the game. Anomalus, I guess, would be viable here for board clear, but it's not worth the cost.

Mulligan for Ice Lance and Frostbolt, and Mad Scientist, or one of your Secrets so you can establish when your Secret usage is most viable. Explosive Sheep is also good for early removal.

This is a slow deck, but it is meant to drag out the fight using your spells against Sapphiron's minions until you can unveil your bigger threats. I've used minimal Deathrattles, most specifically Nerubian Egg since Sapphiron kills it causing it to become a 4/4. It will die next turn however. The same goes for Mad Scientist as he can provide you with some defense between Ice Barrier and Vaporize. Explosive Sheep ensures early removal.

The main spectacle is having Feugen and Stalagg out on the board at the same time. When they die, they will both become 11/11 minions that can take off half of Sapphiron's health. I've tried a situation where I used two Ice Lance on the Thaddius minions, protecting them, and then finishing Sapphiron off.

Spells like Forgotten Torch are amazing and a slight boost to the deck. You can deal 3 damage against a weak minion, then gain a 6 damage spell that can finish or destroy your enemy's minions. 

Hope this helps!