snake and mario are good fighters, but samus and master chief are on another level. mario would avoid snakes shot in a little time with his jumps and agility, and possibly hit snake with at least one punch. we all know mario has good raw power, as seen when he punches things in mario 64. it would damage snake, while mario would get shot in the head shortly after. meanwhile, samus would tool master chief and come after snake. so... mario keeps snake away while samus kills master chief without much trouble, and then samus kills snake, as he´s unarmored.