Arcane Mage

This is mainly a fun deck but it can slowly climb the ladder, depending on the decks you encounter (I reach legend with the bonus star).

Mulligan : only keep the minions (except against rogue who will draw your dragons and Xavius for you) and sometimes Smoldering grove and spark of life, depending on what's beside.

Gameplan :
Play Watercolor artist as soon as possible (using Xavius if needed) and all your minions on the early game to help you stabilize the board.
You can tempo malygos (and sometimes Sindragosa if it gets the reborn dark gift for example) on 5, if it dies you'll resurrect him with Oathstone and if it survives, you'll have a good chance to win on the spot.
Try to play Sindragosa around turn 7 with one or idealy two Buy One, Get One Freeze to kill your opponent on faster matchups and to get your Oathstone against slower ones.
The deck demands a lot of improvisation, depending on your draws, the opponent's board and hp, and even more on your discoveries. For example I usually use spark of life on druid spell on early game and mage later on.

Have fun!