This is a more midrange version of my previous full aggro cancer mage deck found here: http://www.hearthpwn.com/decks/247726-cheap-tempo-aggro-cancer-25-5-rank-95-winrate
After using my aggro cancer deck to climb from 20-6 in no time, I hit the wall that is rank 5. And so began a battle with RNGesus which ended with more salt and close calls than I can remember. After my failure to pass rank 3 multiple times, I changed my tune to oil rogue for a bit, but came back to the tempo mage idea after long games and close calls became annoying.
This mage deck focuses on early game Flamewaker / Mana Wyrm / low cost spell tempo power followed by a Fireball / Frostbolt / Archmage Antonidas / Dr. Boom finisher. The Azure Drakes and Arcane Intellects should keep you afloat in terms of card draw, and you should be able to crush many meta matchups in no time.
In terms of mulligan, generally keep Mad Scientist, Mana Wyrm, and efficient earlygame removal depending on the matchup, such as a Flamecannon / Frostbolt for Shade of Naxxramas / Imp Gang Boss, Knife Juggler, or Animal Companion.
If you don't have antonidas, he can be replaced with Rag perfectly. If you own neither, you'd have to go with something like pyroblast which is really clunky in comparison, but can still provide killing power. Keep in mind nobody really uses pyro for anything these days so I'm not sure how it will affect results.
So far I have had great results, and will make legend by tomorrow at this rate. Don't hesitate to rate the deck so I will feel inclined to add / update it and answer any questions.
Good luck in the ladder!
5/23/2015 Edit: -1 Piloted Shredder -1 Azure Drake +1 Mechanical Yeti +1 Emperor Thaurissan . A few comments suggested these changes and after ~25 games of testing the changes seem to create more winning opportunities. The extra spare part works well with Antonidas and the 1 or more cost reduction on low cost spells from Thaurissan can create ridiculous synergy with Antonidas / Flamewaker.
5/27/2015 Edit: Finally made legend.
Change: -1 Mechanical Yeti +1 Kezan Mystic , just filling the tech slot with something more successful, helping me pull off an awesome set of wins to get me to legend at last! Good luck to anyone else attempting the final push! My final push stats from ~rank 4 to legend are found below.
5/29/2015 Edit: Have been climbing legend well