Level 21: Oberon Iron Mine
Enemies: Class 1 Drone, Medium Hulk, Super Hulk, Medium Lifter, Driller, Heavy Driller, PTMC Defense Prototype, Supervisor Robot
This level is fairly straightforward although there are several doors of the same color. When you see the Hostages through the grate fly up through the secret hatch in the roof to find the prison entrance.
The Blue Access Key is found out in the open in one of the wide hallways. Head through one of the Blue Doors and when you find the open pit with lava at the bottom fly down and pick up the Yellow Access Key at the end of on of the lower passages.
The Red Access Key is in a hallway with Robot Generators. The generators activate when you collect the key. If you’re quick you can grab it and make a run for the nearest door without taking any damage. Head through the Red Door to the reactor room.
Reactor: There are Robot Generators to the left and right that will activate about three times when you try to enter the room. The reactor itself is closed off until you fly over the activation points to open up the barrier around it. To trigger the barrier to open fly through the entrance, into the alcove on the opposite side and then into the alcove on one of the sides that has the Cloaking Device.
Exit: Head out through the Red Door with the Energy Center on the other side, through the next door around the corner and down the stone corridor. When you see the Yellow Door in the distance pull up and shoot the wall to find the Secret Exit.