- This level occupies the map slot MAP16. For other maps which occupy this slot, see Category:MAP16.
There is only one enemy the player can actually fight in this map - a deadly Evil Marine, the eponymous "Mr. X", who will make occasional appearances before the real fight near the red key. He is very fast and armed with a plasma rifle.
There are several Imps scattered throughout the level, but the player cannot fight them. They exist only in sectors with crushing ceilings, which are triggered immediately before and after the Evil Marine first appears. The player can only listen as the Imps are massacred, the implication being the Evil Marine is slaughtering them.
- After getting the yellow keycard, open the yellow bars and shoot the lights to your right. This opens one piece of a misaligned wall to your left. Inside you can get 9 Health Bonuses and a Combat Armor.
- Pressing the left switch in the room of secret #1 opens a small chamber behind the blue bars with a Backpack inside.
- In the room with many boxes, go behind the right set of boxes and climb them. Then jump towards the other set where you can see a Shotgun on top and get it.
The Compet-N records for the map are:
|Monsters||ITYTD and HNTR||HMP||UV and NM||MP on UV|
|Powerups||ITYTD and HNTR||HMP||UV and NM||MP on UV|
|Weapons||ITYTD and HNTR||HMP||UV and NM||MP on UV|
|Ammunition||ITYTD and HNTR||HMP||UV and NM||MP on UV|
|Keys||ITYTD and HNTR||HMP||UV and NM||MP on UV|