This is something that would be perfect to train Spartans instead of teaching them to fight each other in the simulator.
Conquest
If you have ever played Galactic Conquest this is basically that but in an FPS RTS version. It is a 4v1 map jumping Firefight. 4 Spartans defend against a Covenant Invasion.
Just like Galactic Conquest each planet(or map) player obtain earns them abilities and advantages to fight against but they can only choose one planets ability for each battle.
The Spartans can only attack after they successfully defend against an assault from the Covenant. They will have to evacuate civilians, rally UNSC troops and defend key zones of interest away from the Covenant forces.
While the Covenant Commander chooses these areas to attack and leads the ground forces to them. Killing or routing the Covenant leader will the Spartans the option to attack. The Assault the Covenant Leaders Battleship fight through its defenses and assassinate the Commander.
Along the way the Spartans will be assisted by UNSC forces in 3 ways. Troops, Weapons or Powers. After earning points Spartans can ask for 3 things.
Allied support from the Army, marines, ODST or other Spartan IV AI (depending on how many points they have) to move in and assist them in the battle.
Weapons of course will give the Spartans a weapons drop of ammo, stand UNSC weapons along with 4 heavy weapons of their choosing.
Powers will let the Spartans use the abilities they got from other planets. Powers range from artillery rounds to bomb areas, EMPs to knock out all tech, and bombing runs.
If the Spartans are routed they can pull back to their defenses and assist before the Covenant forces return but if they are killed. They Covenant commander can begin their assault on the base and the Spartans must hope that their defenses are enough to fight off the Covenant threat.
Covenant abilities are split into 3 as well.
Special Units- These are the abilities the Covenant will get from taking over worlds. These units will range from Black Ops Strike Teams to a Scarab.
Personal Intervention- The Covenant Commander can use the points that they have gained or if in mass failure to deploy themselves to the battle. They will have 2 Honor Guards will them at all times, a Phantom for extract(unless shot down) and they will have 2 times Overshields.
Full Assault-If the Covenant Commander takes out one of the 3 UNSC bases in the match they will get the ability to send troops to attack in full force. Multiplying there normal unit count by 4. The troops will fearlessly charge one of the two remaining bases and hold it until it is taken from their cold dead hands.
After 4 Planetary Victories each faction will be able to choose their factions special ability. The UNSC can have a full on assault take a a hostile world from the clutches of the Covenant putting it in their safe hands and the Covenant can order the total Glassing of any world under human control rendering the map non-accessible for the remainder of the game.
Each faction will also have a key planet to attack and that can’t be affected by the factions special ability only planetary. For the UNSC they will be able to start an operation similar to Red Flag. To Begin an attack on the Covenant Leadership and wipe the Covenant out at the heart.
But if the Covenant push the Humans back they get to Assault and destroy Earth.