This has been around my mind for a while so I decided to share it here.
It would be like normal Invasion (capture territories, destroy targets etc.) BUT, one major difference is that you play as ANY character of the side you are. For example, if you are on the Human side, you would randomly spawn as a low-ranked marine, an advanced marine with more armor, maybe ODST, and Spartan. And for the Covenant, grunt, jackal, elite etc.
Or maybe even Prometheans would be awesome too! Imagine an Invasion match: Human vs Covenant vs Prometheans vs Flood! That would be incredible for us to see/play! Like the Humans defending their base form the Covenant and the Flood trying to sabotage or kill everyone, while Prometheans try to stop them!
Now for the balancing part, players have 1~3 loadouts to choose, depending on their rank.
I know that the only problem is the game balance, the gametype would work well, I believe. Post your thoughts or your ideas