[Update: This combo is legit crazy enough for Mark McKz. His deck is here. He called it "surprisingly fun." Watch his video, below.]
The goal of this deck is not to win as fast as possible, but to win with fire. Here's the plan:
In order to have a 0-cost Ragnaros hero power, you have to pop Majordomo Executus before completing stage 2 of the quest. So delay the quest until turn 6 (or as late as you dare), when you also play 3 cheap damage spells. The Rag hero power does not seem to benefit from stage 1 completion; it will always only target random enemies.
Use the Sphere to not draw the deathrattles. If you haven't found Boom-Zooka by turn 6, maybe use the Sphere to take a chance on finding it.
Play Boom-Zooka on 7 (which ideally puts you at 24 life), complete the questline, and enjoy your new hero power, DIE, INSECT!. Note that Ragnaros will remove any armor you gain, so if Majordomo dies last, you get none.
Obviously, the big tricks to this are 1) surviving until turn 7, after having crippled your opening hand; and 2) drawing Boom-Zooka before drawing your deathrattles. To a lesser extent, there's also the challenge of having enough spells to refresh your hero power. So, spells that generate spells are useful for this gameplan.
Here's Mark McKz killing his opponents with style. And fire.