Peter Dinklage, Pedro Pascal Peter Dinklage, Pedro Pascal

Trust a Dornishman to get excited by impossible odds.

On Sunday's Game of Thrones (9/8c, HB), Oberyn Martell (Pedro Pascal) will enter into trial by combat against Gregor Clegane, who is nicknamed The Mountain for his ridiculously vast size. The series cast massive Icelandic strongman Hafthor Bjornsson to dwarf his onscreen competitor. "He's nearly a foot taller than me. He's 6-foot-9; I'm 5-foot-11," Pascal tells "I think he's nearly three times my weight. He's 420 pounds of muscle. It felt like I was with a giant. And then put him in the armor, and his sword alone was exactly my height. It was incredibly intimidating but also really delightful because I think that the character Oberyn really relishes that kind of challenge."

PHOTOS: Hot summer TV eye candy!

Of course, part of the reason Oberyn is fired up about the face-off is that he will finally get vengeance for the rape and murder of his sister and the deaths of her children by Clegane. But what chance does a lothario like Oberyn have against such an intimidating foe?  Sunday's episode, titled "The Mountain and the Viper," may give a clue to Oberyn's other physical skills. "Well, somehow he's gotten that nickname 'the viper' from fighting," Pascal teases. Indeed, a preview for the throwdown shows that the agile Oberyn is no stranger to going toe-to-toe against a worthy opponent.

But let's not forget what got him into this position in the first place. After Tyrion (Peter Dinklage) demands a trial by combat to determine his guilt or innocence in killing King Joffrey (Jack Gleeson), Oberyn visits him in his prison cell to offer his services as a champion. "It's not hard for Oberyn to recognize that Tyrion is the smartest man in the room," says Pascal. "Oberyn is not a fan of the Lannisters, so it's not very hard for him to see through the trial and recognize what's really going on. And while he has his own agenda, because he wants nothing but to face The Mountain himself and kill him, to be able to do that on behalf of Tyrion is an extra 'f--- you' to the Lannisters because he recognizes to Tyrion their hypocrisy and their corruption."

Must-see summer flicks

Oberyn's big gesture follows an impassioned speech in which he tells Tyrion of how he once visited Cersei (Lena Headey) as a child and saw her abuse and insult Tyrion as an infant. As the story unfolds, we can see the anguish and heartbreak on the Imp's face. (Revisit the scene here.) "I was very moved," Pascal admits. "It was my first day on set so I was really quite nervous. But then I had this wonderful, compassionate director Alik Sakharov and Peter Dinklage, a completely generous and welcoming actor. I don't know if I realized that the scene climaxes with such strong emotion. It was deeply moving for me to tell Tyrion the story and to see Peter Dinklage receive it. It fed me in a way that I'll never forget."

Although Tyrion and Oberyn may not be friends exactly, they do share a mutual respect that could lead to a beautiful bromance. "I think there is a little bit of a kindred spirit between the two of them," Pascal acknowledges. "Oberyn can recognize that Tyrion is a survivor and that's through cunning and intelligence. Also the two of them can also relate to the fact that they love to have good times! If they could stay alive together, I bet they'll be really great pals."

Are you psyched for the big fight?

Game of Thrones airs Sundays at 9/8c on HBO.