E3M4: All the Marbles (Serenity)

E3M4: All the Marbles is the fourth level of Serenity. It was designed by Bjorn Hermans and Holger Nathrath, and includes a custom music track.

Essentials
Take all needed items and enter any door. Go south along the corridor with cage and use the western alcove. Use the teleporter at the end of it. In the outside area which is behind the cage, use the staircase leading to the door. Press use on any computer panel to get inside (note that pressing will open the opposite panel). Once done with that, bump against the eastern panel to unlock the red skull key (you might want to bump against other walls to unlock various optional items).

With the key, leave the computer room and in the outside area, go through the red door. Some crushers and platforms will work in this room. Get to the opposite side and then around the corner. Open the baron door. In the familiar corridor, head very south and drop down to the pit. Along the corridor, head into the eastern room. You can notice two pillars and some barrels there. Press the switch in that room. Backtrack to the place when you have dropped. You should now notice an open alcove. Enter it and press the skull switch to your right. Now, backtrack to the eastern alcove towards the eastern room to reveal an "E" letter with the yellow key on it. Grab the key and escape via the southern room. Enter the fiery teleporter.

Walk upstairs and open the brightest wall at the end. Open the red door. To your left is the structure which has the staircase behind it. Use that stairs and flip the switch to open one of the doors. Head thru that open door and open the yellow door. In this maze you should get to the south of it and press the switch which opens the second door in the previous area. To do this, head all the way west, south, east, south, east and then south. Press the eye switch in the dead end. Backtrack through the maze towards the room with two doors via the yellow door. Enter the opened east door. In the similar corridor, enter the fake wall at the end and flip the switch to beat this level.

Secrets

 * 1) Directly south of the first room is a concave wall.  Open the middle of the wall east of this area to find a plasma rifle. (sector 11) Press the skull on the wall to reopen the door if it closes before you leave.
 * 2) The door used to access secret #1 also counts as a secret. (sector 12)
 * 3) The passage to the teleport pad leading outside counts as a secret. (sector 54) It is lined with nine health bonuses.
 * 4) The teleport pad in secret #3 is also considered a secret. (sector 53) It is thus unreachable, as there is no way to step onto the pad without teleporting away.
 * 5) The passageway containing the switch which allows access to the yellow key is flagged as a secret. (sector 102)
 * 6) The space directly in front of said switch is also marked as secret. (sector 101)
 * 7) The first, unlit space of the passageway to the E room counts as a secret. (sector 127)
 * 8) The lit portion of the passageway to the E room counts as a secret, too. (sector 128)
 * 9) The cage from where the imps attack you in the passage to the E room is also marked as a secret. (sector 125) There is no way to enter the cage, and so this secret is unreachable.
 * 10) The pit that the passage to the E room curves around also counts as a secret. (sector 131) Press the wall at the south of the pit to raise the floor and escape.  On skill 4 or higher, you will find two boxes of ammo here.  Note that on skill 3 or higher, you may have trouble entering this secret, as one half of each opening into the pit is blocked by a barrel.
 * 11) The window immediately south of secret #10 counts as a secret. (sector 175) It cannot be reached, as you can neither climb nor fit through the window.
 * 12) The room seen behind secret #11 counts as a secret, as well. (sector 174) It is likewise unreachable, as there is no way to enter the room.
 * 13) The E room counts as a secret. (sector 130)

Bugs
Engine versions prior to v1.666 can display a minor HOM as the red door is opened.

Four of the secrets are unreachable; as a result, only 69% Secrets is possible.

Current records
The records for the map on the Doomed Speed Demos Archive are:

Player spawns
This level contains four spawn points:
 * 1) facing south-west. (thing 230)
 * 2) facing south-west. (thing 231)
 * 3) facing south-west. (thing 232)
 * 4) facing south-west. (thing 233)

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

Inspiration and development
An early version of this map appeared as E2M2 of the collection "Nathrath's Fab Four" (NATHRATH.WAD).