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 )
So heres the elite campaign mod in the second level halo. This mod replaces master chief and all your marines with shangheili elites. This also replaces Covenant elites with covenant brutes. Replaces sniper rifle with beam rifle. However since this is an alien vs alien war their are no assault rifles or pistols. Ill add pics later sorry