Fleet Raid can be found in the Battle section (lower right in your Base)
Here you can fight the AI controlled Fleets of other Players which reward Omega Matter, Prime Matter to upgrade your Interceptors and Weapons and Immortalis The amounts of Matter rewarded depends on the Enemy's Host Ship levels plus a random multiplier. This means that the same Fleet can be worth different amounts of Matters every time you fight them.
You can do at most 50 Fleet Raid fights per day, after which you need to either wait for the Daily Missions Reset or pay 150 Credits to refill them. You can see the amount remaining in the battle selector screen and the time till the reset in your Missions Window.
The Fleet Raids follow a sort of Elo System, which means that the more raids you win, the stronger your next opponent will be. Each of your Fleets has a separate Elo Rating.
The rating system also take into account whenever the player loses a host Ships during battle. Because of this, it is possible to lower the Elo rating by losing 1(or more) hosts Ships and winning the battle
thanks to this unusual game mechanic it is possible to control to some extend the Elo of your fleets. In fact, some
- If you want your Elo rating to rise, you must win a raid without losing a single host Ships
- If you want your Elo rating to drop, you must lose at least 1 host ship during the raid, after which you can either win or surrender it.
It's common practice to use lvl 1 host ships when lowering the Elo, since the low level of the ship will make it to be repaired and ready for another raid almost instantly