Season 7. Ellaria notes that her greatest regret was that Oberyn died for Tyrion at his trial. Later, Tyene tells her sisters Obara and Nymeria that her mother Ellaria told her that Oberyn died because of his carelessness. They are then both killed soon after by Euron Greyjoy.

Who wins the fight between the Mountain and Oberyn?

Prince Oberyn Martell won. He toppled The Mountain, the deadliest swordsman in Westeros. Victory was in his grasp. But merely killing Ser Gregor Clegane wasn't enough.

Is Oberyn better than Mountain?

Technically, the talented Oberyn Martell defeated (and mortally wounded) the Mountain in single combat, but his own careless arrogance allowed the dying behemoth to pull him into a skull-squishing death grip. He lost, but we think his performance is enough to land him one slot higher than his hulking opponent.