At the end of the battle between Prince Oberyn and The Mountain, why didn't The Mountain die? Wasn't he stabbed multiple times in the fight by Prince Oberyn?
In the books, he did die, only from poison, in complete agony, two weeks later. In the show, there is a hint that he died too, because, after the fight with Oberyn, we never see the Mountain outside the armor and without wearing his helmet. Implication was that Qyburn raised him with black magic or something.
“I know the poison that my father used, and there is none slower or more agonizing.” “Sisters, truly, I know the poison Father used. If his spear so much as broke the Mountain’s skin, Clegane is dead, I do not care how big he was. Doubt your little sister if you like, but never doubt our sire.”" Tyene Sand, Oberyn's daughter.
Oberyn wanted to give a painful death to Gregor Clegane.
“And we know that Oberyn wounded Gregor grievously. Every report we have had since claims that Clegane died slowly, in great pain.”
A Dance With Dragons