Getting the Red Key / Getting to the Red Key Slot / Getting the Yellow Key

Code Room: After activating switches in the Red Key room, return to the column with the original code. Hit the new switches in the combination O X X to open a door opposite your position.

Outer Shell 2: Use the Chaingun Cannon immediately due to the number of Troopers. Circle the area to the left to progress quickly, or to the right to face Slimer Eggs and Captains on ledges. The left path leads to a room with Slimer Eggs, two Enforcers, an Alien Drone, and an Octabrain. Collect the RPG, two Large Medikits, two Devastator Ammo, and two RPG Ammo found within this area. A Devastator and Protective Boots are located behind the large column.

SECRET 6: Find a hidden passage resembling a butthole within the large column. Enter it to collect Pipebombs, Devastator Ammo, RPG Ammo, Chaingun Cannon Ammo, and a box of Shotgun Shells. This passage leads to the Inner Shell area.

Inner Shell 1: Access the inner shell via an underwater area containing Alien Drones and Octabrains. Destroy Slimer Egg clusters to break surrounding columns. Emerge in the center of the underwater area. In the inner shell, defeat three Enforcers, three Troopers, and two Alien Drones. Find Body Armor on a ledge. A door will open beside you, revealing a pool with an Enforcer and an Alien Drone. Swim down into the small room beneath the pool (previously guarded by a Forcefield). Collect a box of Shotgun Shells, Chaingun Cannon Ammo, and a Jetpack. Activate the switch in this room to reveal another switch to its right. Activating the second switch opens an underwater door.

Red Key Room: Navigate to the Red Key Room containing three rotating gears and a switch. Carefully activate the switches near the gears. Use the grey divots on the gears for safe passage to a compartment at the end of the room. Collect the Red Key, Atomic Health, and Body Armor from this compartment.

Return and Red Key Slot: Go back to the ledge in the Inner Shell area that had the door with the pool. Ascend to a higher ledge, which will automatically open a door revealing a Battlelord and an Enforcer. Defeat them and collect the two Devastator Ammo. Use the Red Key in the Red Key slot located here.

Yellow Key: Enter the resulting room to find the Yellow Key and a Portable Medikit. A switch in this room raises green columns in the Purple Acid area. Return to the starting spawn point of the level where the Yellow Key is located.