This is my take on what an FPS could be for illuvium. It would be a fairly normal FPS but you can bring 3 illuviuls with you say an Axodon, Scoriox, Rhampyher. They would all still have their affinities and classes and omegas. The battle starts you run around set your Scoriox in a sniper position and it lava field starts to spread. You have your Axodon follow you around as a meat shield and if it goes down it makes the rest of your team stronger. Rhampyher is also following you keeping up a consistent damaging heat field and when an enemy is in sight dives at them and activates it omega.
You can decide this scenario however you want but this is just a partial example of how ane FPS could go for illuvium. Let me know what you think