Criston Martell was killed by the Mountain, but his death is never fully explained.
Ser Criston Martell is a minor character in the first season of Game of Thrones. He’s killed off-screen in the fourth episode, “Cripples, Bastards and Broken Things”. This is a shame because he was a very interesting character who never got to develop properly. In fact, we only know that he exists because his name appeared on Robb Stark’s death list in Season 2.
This isn’t an uncommon occurrence on Game of Thrones. We don’t know what happened to Ser Hugh of the Vale or Ser Rodrik Cassel, both of whom are killed during Season 1. We don’t even know what happened to Ser Gregor Clegane after he was left for dead following his duel with Oberyn Martell. However, there are some deaths that are more notable than others.
The most notable death is definitely Joffrey Baratheon. He has a large role in Seasons 1 and 2 before being poisoned at his own wedding in Season 4 by Olenna Tyrell and Petyr Baelish.
How did Joffrey die?
Joffrey was poisoned by Olenna Tyrell at his own wedding to Margaery Tyrell after she slipped him some poison called The Strangler as part of her revenge plot against House Lannister for the death of her daughter Elia Martell during Robert’s Rebellion. The poison works quickly and kills him within minutes.
What about Criston?
The man who played Ser Criston, Gethin Anthony (best known for playing King Arthur Pendragon on Merlin), revealed that he had been cast as Prince Oberyn Martell before being recast as Prince Doran Martell when Pedro Pascal joined the show.
Why did they recast him?
