Candidate 1: Master chief.

Intro:

Master Chief drives a mongoose into the arena, then jumps off. He looks at his opponent and says 'I'm finishing this fight.'

Costume 1: his armour in halo 4.

Costume 2: his armour in halo: combat evolved. (Mark V)

Victory pose:

Chief gets his assault rifle, fires to the left, then the right, then slings it over his shoulder as he looks at the screen.

Babality: Chief twists his helmet around and starts looking around in confusion.

Fatalities:

(The soldier they need you to be) Chief equips a shotgun and blows the opponent's leg off. While they still stand, he then stabs in the stomach with his knife, and throws them to the floor. Finally, he fires an entire clip of the assault rifles into the opponent's head. Chief then stands at ease with the same rifle.

(Reinforcements) Chief drives a warthog straight into the opponent, then climbs into a scorpion tank. After blasting the opponent's lower body into nonexistence, he then pilots a mantis, then stamps on the still-crawling opponent. The mantis then fires missiles at the air in triumph.