The developers have stated many times that the buff to C'Thun works more like an aura than an actual buff so I was wondering this: can C'Thun be silenced if I somehow survive the initial onslaught? What happens then? Does the silence remove the whole buff from C'Thun (wherever it is) or does it just fizzle?
You can silence an in-play C'thun to revert it to a 6/6.
However, if a silenced C'thun later gets sent back to its owner's hand or deck, it will regain its buffed stats.
The aura still applies to cards like Klaxxi Amberweaver, which check for C'thun having 10+ Attack, as reported here.