For the UNSC. We need a jet, to a longsword but more conventional, twice as fast as a boosting saber, the dogfights would be the bomb! And if anyone got the MMM Main Menu Mod (legal) in Halo 2 pc. There was a black ghost that was two times faster, but only shot strong grav lifts. But out the front so you went FLYING, maybe with on that a little?
Do turrets count? If so, adding the fuel rod turret and a rocket turret (like the rocket hog) would be good
What about the flood as a playable race with giant controllable flood creatures to ride. You could have a 3 team territories like gamemode where all three factions battle over a piece of land.