MAP24: The Mucus Flow (Community Chest 2)

MAP24: The Mucus Flow is the twenty-fourth map of Community Chest 2. It was designed by B.P.R.D, and uses a music track composed by him. It is notorious as the hardest level in the megawad, and is also impossible to complete in Boom as the result of a design flaw (see Bugs).

The level is set in a rocky outdoor area, with a river of green mucus flowing through it, and within a techbase flooded by the substance. There is no health or ammo to be found on the way, other than within small depots scattered throughout the level, most of which require a well-guarded key to access.

The Mucus Flow was featured in Doomworld's Top 100 Most Memorable Maps, placing 3rd.

Essentials
The large shack behind your starting point is of vital importance, as supplies are extremely scarce in this level bar this one shack. Whenever you need health or ammo, you will need to come back here. If you went for the valley that houses the red key, then you need to be wary of a monster in this shack (an arch-vile on Ultra-Violence, for example) The switches on the eastern side house weapons, and three of them are colored key switches, so you need to hunt for keys to get them. In a technical sense, you will not need any keys if all you want to do is get through the level, but they are vital if you wish to survive through to the end. From the start, go west, through the building and keep going west through the valley. Ignore the tower guard zombies, as they will respawn and you will not have enough ammo to kill all of them. Pass through until you hit a fork, you will have a few options at this point:

To get the red key, head right and then left at the next fork, and then go through the next valley. There is a health shack here if you need it. Be wary about your health and ammo, and watch out because some enemies may come through the slime falls. When you reach a large slimefall which seems to be a dead end, look for where the rock juts out and you will see part of the slime fall is misaligned. This is an opening so you can continue through the valley. Keep climbing and you will eventually find the key.

If you are heading for the blue key, head right at the fork and then right again, following the path. You will enter an area with a cage to your right and nukage on the floor. There is an opening through the slimefall where you can reach the lift. Enter through to the big area and climb onto the little crates into the valley here to get the key. Climb the stairs to get back out.

If you are heading for the yellow key, head left at the fork. Take either path and hit the switch to reveal an area behind you with a fountain. Be extra careful here, as chaingunner closets will appear in the walls after you move over some linedef, and some demons will come from behind. The switch near the door opens it into the next hallway. Take the first door on your left. Here there are some areas where if you cross the blue lines, imps will teleport. The yellow key has a lot of monster teleports, some of them are mancubi.

If you are just getting out, take the yellow key path, but keep going down the long hallway, through the next room into the next valley. You will have to traverse this long valley until a long lift, then continue through the upper reaches of the valley. There is a health shack at the bottom of the valley, and an ammo shack (guarded by revenants) a bit past the elevator. You need the red and the yellow keys, respectively, to open them. Crossing the blue line near the pads will cause revenants to teleport in. You will reach what eventually is another dead end, but go through the slimefall to find another switch here. Pressing it floods the valley with nukage. Now go back all the way to the entrance of this valley until you find an opening close to where the health shack was (also take note that the health will be openly available if you have not picked it up yet. Go through this winding road and exit by approaching the column with the stars on it.

Secrets

 * 1) At the bottom of the stairway at the south of the silver building, southeast of the lift, one of the nukage falls on the south wall can be walked through.  Do so to find stairs leading to two sets of shells and three stimpacks. (sector 1287)
 * 2) Near the doorway at the southeast of the silver building, look toward the east wall to find an arrangement of small gems in the walls, accompanied by a larger one.  One of the small gems is slightly larger than the others.  Press on it to open a door nearby. Follow the path beyond the door until you find a switch.  Press the switch to activate the elevator, which will take you to eight stimpacks, five medikits, two boxes of ammo, two boxes of shells, a blur artifact, a berserk pack, and a computer map, all gathered around a giant nose with nukage flowing from its nostrils. (sector 1556) Behind the nose is a teleporter, which you take you back to the previous room.  You can only enter this secret once.
 * 3) In the room before the room where the yellow key is found, the monster teleporters inside, unlike the ones in the other two rooms, are connected directly to the eastern wall.  Press on the portion of that wall south of the wire to find a teleporter.  Use it, and you will be taken a cliff high above the blue key area, where you can jump to a brown structure containing a soul sphere. (sector 384)
 * 4) In the hallway north of the yellow key area, the windows are bordered by small gems in the wall.  The westernmost one is slightly larger than the others.  You are meant to be able to press under it to lower the wall, and access the nukage-filled area beyond.  (sector 884) At the east side of this area, you can find seven stimpacks.  However, linedef 13930, the south side of the secret lift, cannot be activated, as there is a special line in front of it, linedef 8862, which is of type 85 (animated wall, scrolls right,) but does not have PassThru set.  As a result, this secret and secret #5 cannot be reached unless you are playing in a ZDoom-based port, or the noclip cheat is used.  Users of PrBoom+ can turn on "Use passes thru all special lines" in order to activate the lift.
 * 5) Inside secret #4, the southwest side of the northwest nukage fall can be walked through. Climb over there, and do so to find a corridor leading to a switch. (sector 1971) Upon flipping the switch, all of the enemies to be teleported into the towers near the beginning of the level (who account for 517 of the map's monsters on all skill levels) will be killed, allowing you to take out their previous occupants without having another teleport in their place.  Outside of a ZDoom-based port, or use of the noclip cheat, this secret cannot be reached for the same reason as secret #4.
 * 6) Three crates in secret #5 are each marked as secret, but are impossible to trigger apart from using the noclip cheat, as there is no way to climb onto them. (sector 1973)
 * 7) See above. (sector 1974)
 * 8) See secret #6. (sector 1975)

Bugs
Linedef 9094 (the switch opening the four doors outside at the north of the map) is located closely behind four linedefs (9956, 9957, 9958, 9959) that are of type 48 (animated wall, scrolls left) but are not set as PassThru. Thus, the switch cannot be activated, rendering the level impossible to finish, unless you are playing in ZDoom, or the noclip cheat is used. Users of PrBoom+ can activate "Use passes thru all special lines" in order to reach the switch.

On skill 2 or lower, the landing spot for the teleporter in secret #2 does not exist, making the secret impossible to leave.

Because five of the secrets cannot be reached, with two of them unreachable because of a similar bug to the above, you can only obtain 37% Secrets on this level. With the issue corrected and those two secrets reachable, only 62% is possible.

Current records
The records for the map at the Doom Speed Demo Archive are:

The data was last verified in its entirety on April 3, 2022.

Player spawns
This level contains four spawn points:
 * 1) facing west. (thing 2211)
 * 2) facing west. (thing 2212)
 * 3) facing north. (thing 2213)
 * 4) facing east. (thing 2214)

Things
This level contains the following numbers of things per skill level: