I'm going to assume 1 C'thun card for each class and 1 neutral C'thun card for each mana cost from 1 to 7. This gives us 16 total.
C'thun Primus CC = 1 A/H = 2/1 Text = Give C'thun +2 attack no matter where he is. Thoughts = Sort of a riff off of Abusive Sergeant.
Beckoner of Evi
C'thun Quadrus CC = 4 A/H = 5/4 Text = If C'thun is in your deck, Draw C'thun Thoughts = This text is almost necessary for a C'thun deck to be successful. It give you 3 chances to draw C'thun by turn 8. I chose the 4 mana slot because it is one of the most important slots in Hearthstone and I felt this ability was the most important to C'thun decks.
C'thun Quintrus CC = 5 A/H = 3/2 Text = Your hero gains life equal to C'thun's Health no matter where he is. Thoughts = You are going to need some staying power to get to turn 10 to cast C'thun. This card is a riff off Antique Healbot and gives you some staying power.
C'thun Sextus CC = 6 A/H = 4/6 Text = Taunt. Give C'thun +3/+3. Thoughts = You'll need some more staying power to get to turn 10. This gives you a taunt and a big boost to C'thun.
C'thun Septus CC = 7 A/H = 7/7 Text = C'thun costs (2) less. Battlecry: C'thun gains +1 attack for each friendly minion in play. Thoughts = This lets you curve right into C'thun and makes him win more.
Then the class cards ---------------------------------- C'thun Magus CC = 6 A/H = 5/3 Text = Deathrattle: Deal 1 damage to a random enemy for each attack of C'thun no matter where he is. Thoughts = It's a riff off Goblin Blast Mage.
C'thun Rogus CC = 2 A/H = 3/2 Text = If C'thun has 8+ attack, return a minion to it's owner's hand. Thoughts = Sap on a stick.
C'thun Paladius CC = 6 A/H = 6/6 Text = Battlecry: Give C'thun +1/+1 for each Silver Hand Recruit that died this game. Thoughts = I thought it would be nice to give Pally a new Dr. 6.
C'thun Warrius CC = 3 A/H = 2/3 Text : Battlecry: C'thun has Charge. If C'thun all ready has Charge give it Windfury. Thoughts = Sort of a tribute to Warsong Commander.
C'thun Shamanus CC = 0 A/H = 3/2 Text = Overload 2. When you play a card with Overload give C'thun +3/+2. Thoughts = Just some craziness.
C'thun Priestus CC = 2 A/H = 0/5 Text = Taunt. Give C'thun +1 attack for each point of damage this takes. Thoughts = Plays into healing and buffs.
C'thun Huntus CC = 4 A/H = 6/2 Text = If C'thun has 10 or more attack give this Charge. Thoughts = Opens up combo Hunter.
C'thun Warlockus CC = 5 A/H = 0/3 Text = Stealth. Whenever C'thun gains attack this gains +1 spell power. Thoughts = Gives you a Malygos type flavor with C'thun.
Getting creative with names I see :) (shouldn't it be Quintus by the way?)
Warrius seems too strong, just putting a 10/10 charge on the board like that (next to the timepiece battlecry). Huntus... uh... ok, charge, sure. I like Shamanus, seems pretty good.
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I'm just another one of those. You know, those who do things. Things that need to be done by those that do these things in order to do those things that don't do these things themselves. Has the word 'things' lost meaning to you already?