Hearthpwn

This is a slightly upgraded, or in other words more expensive deck based on the popular "Budget C'thun" deck by Paylesscss.

I had great success and a pretty easy road to rank 5 last season. 

Mulligan for Mana Wyrm, Beckoner of Evil, Cult Sorcerer and Twilight Elder. 

A great early combo is Cult Sorcerer + Coin + Arcane Missles if you have low health enemy minions to remove. Always try to combine Cult Sorcerer with a spell likeFrostbolt. 

Your spells are your key to board control, removing annoying Deathrattle minions (Sylvanas for example) that are around with the N'Zoth decks with yourPolymorph or big drops with yourFireball, currently mostly used for Flamewreathed Faceless combined with your hero power easy 7 damage, or with one of your spell damage minions.  

Brann Bronzebeard for a Arcane Intellect
Twin Emperor Vek'lor for Doomcaller
Crazed Worshipper for Sen'jin Shieldmasta

See the original decklist here:
http://www.hearthpwn.com/decks/503285-budget-cthun

If you have suggestions or additions please leave them in the comments!