Not sure if this is already known and unfortunately i do not know how to post pictures so i did not take any. In single player tombs of terror plague of madness level 2 normal (not heroic). The plague lord was seemingly wrongly getting a second emperor as it was displaying his C’thun at only 8/8. Happened 2 turns in a row and left it with 12 health (gah!). I can’t be certain whether it was just displayed wrong or actually mechanically wrong. Also worth noting, I was playing on an Amazon Fire HD 8 (which has been very buggy lately anyway). Please take my word for it and look into it?.. Thanks
There is a sticky on how to post links.
Using that to refer to wiki on C‘thun:
https://hearthstone.gamepedia.com/C%27Thun
When exactly C’thun related cards can activate is a bit complicated - especially with other not C’hun related buffcards involved. Read the wiki to get more information on that…
It should not have activated as C’thun did not yet have 10 attack
Like Nirot said, it can get complicated. Are you SURE the opponent had not played cards which buffs minions in the deck? Also, was the C’thun on the board, buffed by something else so that it had more than 10 attacks? Or, was it in hand, and buffed by a hand buff effect like a minion or spell which gives all minions in hand +1/+1? Any of those effects do not show in the current values of C’Thun (which is shown, say, when playing the Twin Emperor), yet the C’Thun could still have at least 10 attack, and thus allow the Emperor to summon the second one.
I can’t say for certain but I am nearly positive C’thun had not been buffed in any other way since it was still so early in the encounter when the Emperors were played so he had to still have all of his mana crystals… Again can’t say for certain but still think it is worth looking into… Sorry to be possibly blowing smoke…
Provide more details and we may find a real bug, but as it is currently, it seems to be a dead end as it can’t be replicated. Currently, one card that the plaguelord runs that can buff c’thun “secretly” would be Surrender to Madness.
Right definitely posdible maybe i misremembered the sequence of events since it cant be replicated… Thanks for checking