Hearthpwn

This deck focuses on stalling until turns 8-9 when you can play Medivh, the Guardian and/or Frost Lich Jaina. From there you make use of your super swingy Elementals, spells, and Hero Power, and push for face damage as much as you can, only removing potential threats (if you're playing against a deck that probably runs Bonemares, every creature is a threat). Dragoncaller Alanna is actually a pretty good card in Priest-heavy metas, and it's pretty easy to get an 18/18 or 23/23 Alanna.

While Pyros isn't a must have, I would classify Baron Geddon and two Arcane Tyrants as vital staples to the deck. Arcane Tyrant is an incredibly swingy card that lets you either develop much quicker or swing a board state in your favor much faster. Be careful when playing them, though, you don't want to play a Flamestrike into a board that has a 5/5 or something if you can't ping. In that situation, save your Tyrant(s). Baron Geddon is vital because it's good on its own but incredibly powerful with Frost Lich Jaina and can potentially win you the game flat out.

Also, Deck of Wonders is by all means not necessary. You could sub it for Cabalist's Tome, but I don't love the idea of that in this deck. It could be fine.

Yes. Rummaging Kobold would be funny. But not good.