The Mirror event for the FED and KDF is a relatively straight forward mission.
Defeat the 4 Mirror universe squadrons
Optional: Upload a Virus to the 4 satelites in the shipyard if successfull the ships will be damaged when they emerge during the final scene
Defeat the Flagship and it's hopefully damaged escorts.
A fairly simple exercise with two quirks.
1. The Optional does Not provide a reward if it is completed other than damaging the ships in the dry docks
2. If the satelites are activated before the squadrons are engaged then the squards will move to secure the satelite and cause the mission to fail. This can lead to the Spawn point being overrun by two or more squardrons of ships. Not fun.
The Difficulty lies in timing completion of the Optional task without overloading the spawn point.
First Engage and Destroy Squardron Alpha then Beta. Once Destroyed Move to Engage either Delta or Gamma and send one fo your team members to activate the all fo the Satelites. By the time your team has destroyed the remaining two squadrons the virus should be uploaded and successfull.
The Flagship will appear in a cutscene, I like to hit the Stadi with power drains to slow it down and the destroy the damaged ship that are coming out of the shipywards. Once the damaged escorts are dead take down the Stadi, Disable Shield Systems are nice at this point since its shields are pretty resilient. Also try and stay out of it's front arc, it is a Dreadnought and will happily hit you with it's phaser lance.
The rewards are typically an item and 480 Dilithium.The skill points for killing the enemy ships are especially nice for leveling an alternate character.
The common question regarding the Optional task is why bother? Or Why not just race around uploading the virus immediately?
Simple: these events only last for one hour, thats 60 minutes. I have successfully cleared this mission in 10 minutes with a good team and I usually average around 15. That means I can run this mission and all of its rewards in skill points, dilithium and items at least 4 times. That typically results in 1-2 levels for an alternate character and 1920 dilithium plus items that drop.
By doing the satelites correctly, the ships during the final scene are weakend and go down extremely quick, AND I do not have to deal with the Spawn point turning into a death trap because Alpha, Beta, and Gamma Groups are sitting on top of it as I re-spawn. When this happens this mission can turn into a long desperate grind that can last for 30 and even upwards of 45 minutes on a bad day.
So please.. Kill the first two groups, then hit the Satellites, and then kill everything else and enjoy the rewards.