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.)

Walkthrough

 * Letters in italics refer to marked spots on the map. Sector numbers in boldface are secrets which count toward the end-of-level tally.

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 on the Doomed Speed Demos Archive are:

Recorded in ZDoom 2.0.63a.