I feel like I was picturing the fight with Oberyn going into it to ruin but having the poison as a backup plan, trying to get his surgical cuts in to ensure victory no matter the outcome. I feel like fully jamming a spear into someone's chest and causing internal bleeding and probably puncturing a lung based on depth of penetration isn't going to leave me surprised that the Mountain dies of poison but very much surprised that he had the blood pressure to even move afterwards, or that the exertion he used to move didn't force an air bubble from his massive chest wound into his brain and cause an aneurysm, or that that exertion didn't further cause him to bleed out from increased heart rate through the gigantic fucking chest wound that he suffered, or drown in his own blood. That area is pretty well protected internally for a reason but other than that I thought that the fight was a good duration and was probably like ripping off a band-aid quickly for non book readers. Don't keep their hopes up too long about their new A team member.
Qyburn says Oberyn used manticore poisoned enhanced with black magic and part of its magic keeps the Mountain alive to draw out his suffering. So as soon as he was pierced the magic could have taken effect animating him.
"Ser Gregor." Qyburn shrugged. "I have examined him, as you commanded. The poison on the Viper's spear was manticore venom from the east, I would stake my life on that."
"Pycelle says no. He told my lord father that manticore venom kills the instant it reaches the heart."
"And so it does. But this venom has been thickened somehow, so as to draw out the Mountain's dying."
"Thickened? Thickened how? With some other substance?"
"It may be as Your Grace suggests, though in most cases adulterating a poison only lessens its potency. It may be that the cause is . . . less natural, let us say. A spell, I think."
Is this one as big a fool as Pycelle? "So are you telling me that the Mountain is dying of some black sorcery?"
Qyburn ignored the mockery in her voice. "He is dying of the venom, but slowly, and in exquisite agony. My efforts to ease his pain have proved as fruitless as Pycelle's. Ser Gregor is overly accustomed to the poppy, I fear. His squire tells me that he is plagued by blinding headaches and oft quaffs the milk of the poppy as lesser men quaff ale. Be that as it may, his veins have turned black from head to heel, his water is clouded with pus, and the venom has eaten a hole in his side as large as my fist. It is a wonder that the man is still alive, if truth be told."
also
"Just as Father intended," said Tyene. "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."
