What unit would you create for the UNSC or the banished? Personally I think the Unsc would need a forth infantry unit in the barracks called the Hercules which is an anti infantry/structure unit.
What about a commander with some really unusual abilities:
Commander: New Banished commander
*** Special Ability
Releasing the Nightmare:
The commander can throw flood containers from the skies. The ability deal low damages but on exploding, the containers release flood infection forms that will attack and corrupt the enemies units
Side Effect: The flood infection forms are not controled by the player. They are hostile toward the other players and the user himself. Also, as these flood units are not supervised by any flood inteligence, they are at their feral stage and act like sentinels on the field
*** New Units
Vehicule - AA Wraith
The player can build special wraith able to deal large amount of damage to the Aerial units and the building
Infantry - Jackal
The user possess jackal units that replace the default carabine elites (they can also be upgraded with gauntlet plasma shields)
Aerial - Spirit
The player can now build spirits as carrier
***Special Building
New Turret Upgrade - Cloacked Turret
But in a general aspect the jackal should come back as this is one of the most iconic unit in the halo universe (its like making a starwars film without any droid)