* TV SPOILERS below *
As seen in the final episode of the 4th Season of Game of Thrones, The Mountain is actually alive but dying a slow and painful death due to the poison that was used on the Viper's spear that The Viper used to impale and injure The Mountain, just before dying himself in the ultimate death.
Which leaves me wondering. Did Oberyn ever expect to win the trial of combat (which would mean death of The Mountain in the trial) or did he simply want to make sure that if he were to lose, The Mountain would suffer a terrible and painful death?
Answers from the books will also be accepted.