Instead of playing as Master Chief you play as an elite. You have other elites on your side, fight spartans and marines. Note: this is for Halo PC (Combat Evolved) not Halo CE( Custom Edition )
Heres another mod for the elite campaign mod which continues after the Elite Campaign Pillar of Autumn. You play as an elite and have other elites on your side. When you escaped the Pillar of Autumn you crashed landed on halo, but you and your elites have actually crash landed on grunt territory. Now you temporarily fight grunts, but note these grunts are different and are tougher than you think, some of them even use sheilds. Find your elites and resist any grunt attack. Have fun!