I have 2 scenarios, per the following.
I am playing a standard control Priest deck (without C'Thun) vs a C'Thun Druid.
Case 1:
He keeps buffing his C'Thun until turn 10, when I Entomb it.
What happens if he plays more C'Thun buff cards? Does it keep buffing his C'Thun that I Entombed?
Case 2:
Same as case 1, with the difference that I have C'Thun in my deck, too.
When the druid plays more C'Thun buff cards, which C'Thun will get buffed (if any, or if not both)?
Best Answer
Case 1 and case 2 are to all intents and purposes, identical.
The C'Thun buffs act as an aura on your hero. So let's say to start that the druid played C'Thun as an 8/8. After you entomb C'Thun and he plays another buffing minion, his effect will now say that C'Thuns he plays are 10/10. This is broadly irrelevant (since he doesn't have any more C'Thuns to play), with two exceptions:
Meanwhile, if you draw that entombed C'Thun, he'll just be a vanilla 6/6 since you haven't played any effects that buff your C'Thun. In case 2, when you draw the entombed C'Thun card, it'll be whatever your personal buff level is. (Just as when you draw the C'Thun card that was in your own deck to start with.)
In short: the buffs to "your C'Thun" could be better worded as buffs to "C'Thun cards that you play", and are persistent effects on the hero that plays them, rather than buffing specific cards.