Elemental Odd Mage

On a personal note, I've been having a lot of fun with this deck and have used it to get rank up from rank 20 to rank 3 and continue to increase my rank.

General Strategy:

This deck is a fairly aggressive deck that can be divided into 3 stages:

1. Establishing early board presence through the number of 1- and 3-drops.

2. Maintaining board presence with spell and hero power synergy minions transitioning into the midgame.

3. Stat bombs mainly through 7-drops to reestablish or continue tempo. 

General Mulligan Tips:

The only spell you should keep is one copy of Elemental Allies as to maximize card draw efficiency and, as a result, maximize tempo as this strategy will increase the chances of drawing the tempo-based minions to help establish an early board lead.

The 1-drops of Clockwork Gnome, Fire Fly, and Violet Spellwing are always strong and safe keeps.

Don't keep more than one 3-drop, even if you are on The Coin, as The Coin is more valuable for the spell synergy cards. Black Cat is the best 3-drop to keep, but keeping Arcane Amplifier or Chenvaala is also good if you don't have Black Cat in your mulligan. Flamewaker can be kept in the event that you aren't offered one of these 3-drops in your mulligan and depending on the matchup. Don't keep Questing Adventurer.

Jan'alai, the Dragonhawk is a decent keep to have as a powerful turn 7 that you can plan your hero powers around.