Jasper van Heycop said:
About when you talked about the Mountain not "pressing his advantage"...
Isn't a man in heavy armor with a huge claymore going to take every breather he can get? Even just standing out in the sun like he was is a sweaty, tiring business under all that gear. Maybe he was waiting for Oberyn to tire himself out flipping and twirling around, or make a mistake (like say... getting within leg sweeping distance from a stunned giant...).
I don't think that's plausible.
The fight was not very long. A warrior trained his whole life for fighting in armor is not going to be exhausted that fast. The Mountain would have to fight for longer, more intense periods just standing in the battle line of a pitched battle.
Even if he was feeling a weary, a seasoned warrior doesn't take a breather at the very moment he has his opponent at a disadvantage - like, say, being disarmed or reeling backwards. Time enough to catch your breath after the opponent is dead.
And finally the Mountain is demonstrably able to pick up an armored man and crack his skull after being stabbed through the guts with a spear. It is unlikely he was too pooped to fight because he got sweaty.