Berserker appears in Carnival Phantasm as a comedic reinterpretation of his original Fate/stay night character. He retains immense physical stature and strength but boasts exaggerated traits for humor. His primary role centers on Episode 5, "Berserker's First Errand," where Illyasviel von Einzbern sends him to buy batteries. During this errand, his mere presence and unintentional actions accidentally eliminate multiple other Servants from the Holy Grail War. He unknowingly secures victory through this collateral damage while completing the mundane task.

His characterization emphasizes overwhelming power paired with a childlike lack of awareness. He follows Illya's commands literally and unquestioningly, often causing absurd or destructive outcomes. Despite his imposing appearance, he acts fundamentally well-meaning but foolish. He develops an odd fondness for Lancer, frequently obsessively chasing him and even wielding him as an improvised weapon during altercations, creating recurring physical comedy.

A running gag features his transformation into the tank-like "Berser-Car," highlighting the series' whimsical subversion of the original franchise's seriousness. His actions consistently defy traditional Holy Grail War expectations, reducing the conflict to accidental victories achieved while performing mundane tasks for his Master. His role primarily delivers physical humor and situational irony, contrasting his tragic origins.