4. "The Mountain and the Viper" (Season 4, Episode 8)
Two men enter, one man leaves: That's the brutal, beautiful simplicity of trial by combat. But the climactic duel didn't just pit Oberyn "The Red Viper" Martell against Gregor "The Mountain" Clegane. It took three of Game of Thrones' greatest strengths — roguish fan favorites, monstrous sociopaths, and flabbergasting gore — and threw them into the arena as well. The result? Actor Pedro Pascal's sexually voracious warlord got his skull crushed like a tomato right there on screen. Shock tactic? Yes, and no show does it better.