E2M4: Deimos Lab (Doom)

E2M4: Deimos Lab is the fourth map of The Shores of Hell in Doom. It was designed by Tom Hall and Sandy Petersen and uses the music track "They're Going To Get You". The par time is 2:00.

E2M4 is arguably more difficult than some of the levels which follow it. The open layout distinguishes it from most other Doom maps, which are largely composed of rooms closed off with doorways and connected by hallways. Consequently, for example, fighting monsters in the first room normally alerts imps as far away as the opposite side of the level (due to the gunfire sounds from the player), who begin to close on your position.

This level also features several large enemies, groups of monsters released by triggering traps, and several crushing ceilings some of which are cleverly disguised. The player can lure monsters under the moving ceilings to conserve ammo.

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.E2M4dots.png

Essentials
Walk forward and enter the teleporter (A). Take the first left and continue west across two rivers of nukage. At the end of the hallway, turn north, then west, then south and go through a big metal door (B) to find a lift. Press the button to lower the lift, and ride up to the blue keycard.

Return through the big metal door heading north. When the hallway turns right, follow it but then quickly turn left. Continue north to come to the blue door (C). Go through to see the yellow keycard. Grab it quickly, as the ceiling is a crusher.

Go through the nearby yellow door and turn left. Follow the circular hallway and take the first right, going down a red lift (D). Go around this lower hallway in either direction until you come to a green switch on the inner wall. Click the green switch to raise stairs, and go up. At the landing, there is another green switch. Click and go up; repeat at the second landing.

In the room at the top there is a raised square platform (E). Walk onto the platform to open a tall door (F) back at the bottom of the stairs. Descend the three staircases, go through the doorway you just opened, and teleport.

The hallway ahead features a scrolling graphic behind bars. Walk down the hallway to see the exit door, inaccessible across a pool of blood. Jump into the blood and run to the small alcove (G) just to the lower left of the exit door. Click the skull switch on the south wall of the small alcove to raise a bridge across the blood. Take the teleporter behind you in the north of the small alcove.

You are back to where you last teleported from. Walk out of the teleporter and then back into it to teleport again to the hallway with the scrolling graphic behind bars. Walk down the hallway and across the now-raised bridge to the exit door.

Other points of interest
After you cross the two rivers of nukage, take the first doorway to the right. On your left, you will soon see a lighted computer room containing medikits, a shell box, and a green armor. As you step into this room, however, the floor of the hallway behind you will rise (H), trapping you inside until you hit the switch at the opposite end (I). Not only is this guarded by a group of monsters, but the large central structure is a crusher, activated by walking under it at the east side. Note that you can permanently block yourself from entering this area and secret #5 below: by moving very slowly, you can raise the floor without quite entering the computer room, which permits you to return southward and fall down into the blue corridor with no way to get back up.

On the platform where you got the blue key, click the switch on the south wall to lower the half-high wall to the east. Follow the walkway, through a pair of crushers, until you see a crooked, narrow bridge (J). Carefully cross the bridge to obtain several ammo pickups and a radiation suit. (When first activated, these two crushers can easily be traversed together by running straight ahead. If they have crushed someone already, however, they tend to get out of sync and require more caution.)  To avoid encountering the crushers again, you can jump off the bridge to the north and turn right down the nukage passage (K), which returns you to the start area.

If you turn left at the blue door instead of proceeding straight through, you will come to an alcove with a backpack (L). On Hurt me plenty and higher, a cacodemon is also present.

Note that the yellow door is a single-use linedef on the front (west) side: if a player or monster subsequently activates it from the back side, it cannot be reopened from the front even with the key. This may well confine you to the earlier regions of the map, making the exit inaccessible.

After going through the yellow door, turn left and follow the circular hallway (past the red lift on the right) to a doorway on the left, revealing some curved stairs. Go down the stairs into a room (M) with a short wall on your left, overlooking a pool of lava, and five metal doors on your right. The central door conceals a shell box and a medikit; as you approach these, the two adjacent doors will open, releasing several monsters.

In the tall room with the three rising staircases, there are two small rooms on the north wall, adjacent to the red lift. As you leave the lift, watch out for projectile attacks from the eight imps (I'm too young to die and Hey, not too rough) or twelve imps (HMP) or eight imps and two barons of hell (Ultra-Violence and Nightmare!) inside. Stepping on the two lowest stairs will raise the floors of these rooms slightly (N, O) so the monsters can enter the main room; this occurs even if you haven't clicked the green switch yet. The small room on the left contains a button which lowers the red lift.

Secrets

 * 1) At the start, there is a slightly off-color wall to the right, opposite a blinking light. Go through this hidden door to find a shotgun, a shell box, a bullet box, and a medikit.  Note that you do not have to walk all the way to the shotgun to get credit for the secret (sector 188). If you accidentally pass this up, you can take the teleport at (W) to return to teleport (A).
 * 2) At the far end of the large hall you teleport into from the start, there is a square lift. Go up and around the short hallway to find green armor and a computer map behind an array of tall pillars (P). Walk very close to the short red pillar to the east of the tall pillars (it has a skull on top). The tall pillars will then lower, along with the north wall behind them which releases some monsters. To register the secret, you must walk into the small room to the north (sector 16), which also holds a supply of ammo.
 * 3) As you approach the two rivers of nukage, instead of going straight across, turn left and follow the oval structure around to the right; this route will trigger a large door to the north (Q).  Continue around the circular nukage river clockwise, and go through the new door to find demons, spectres, a soul sphere, and a radiation suit.  (To reduce damage, go to the blue key first and collect the radiation suit in the area behind it, as described above.) (sector 10)
 * 4) The crooked, narrow bridge beyond the blue key spans a rectangular nukage pool; in the southwest corner of this nukage pool is a platform (R) with a berserk pack (sector 165).  You can also reach this platform by going southeast from the circular nukage river, through a blue-floored passage.
 * 5) After you cross the two rivers of nukage, take the first doorway to the right. A door ahead on your right will close (S). Shoot it with an impact weapon to reopen it. Go through to find a blur artifact and a chaingun. (sector 120)
 * 6) In the room with the pool of lava and five metal doors, go through the rightmost door. There is a compartment across a nukage pool with some barrels; explode them from a distance. At the back of this compartment is blue armor. (sector 107)
 * 7) In the room with the pool of lava and five metal doors, the leftmost door will open as you approach the nukage pool in front of secret #6.  Go through the leftmost door and follow the hallway around to a room with armor bonuses, health bonuses, and a few other items (sector 53).  As you enter this room, a section of the floor will rise to block the doorway (T), possibly pinning you to the ceiling, so run to the far wall immediately.  A door on the east side of the room, indicated by a green texture, allows you to get back to the hallway.  Note that the trigger for the leftmost metal door only works once, so if the door is subsequently closed from the back side, you can only reach this area via the lava pool (see secret #8 below).
 * 8) In the room with the pool of lava and five metal doors, hop over the short wall at the west end to find a platform with two medikits (sector 36).  To escape the pool, cross to the extreme eastern end and push the wall to raise a secret door (U).  This leads to the hallway in front of secret #7.
 * 9) After going through the yellow door, turn left and follow the circular hallway past the lift on the right and the doorway on the left. In the easternmost part of the hallway, the wall separates slightly from the floor. Drop down into the gap and push the wall to raise a secret door (V). Inside, find a plasma rifle (sector 19) and a teleporter to the raised square platform at the center of the three rising staircases.
 * 10) After you get close enough to the exit door to touch it, turn around. Another section of bridge will rise, enabling access to a soul sphere (sector 182).  Note that if you fall into the blood between the two bridges after both are raised, you cannot get out.

Bugs
Two "hanging torso" decorations (Things 202 and 204) have no flags set for any of the difficulty classes, so they do not actually appear in the level.

The north edge of the exit bridge (linedefs 934, 935, and 936) is tagged to the bridge (tag 16), even though the linedefs have no associated actions.

Sidedef 667 is missing its upper texture. This causes the ceiling of the lava room to bleed into the ceiling of the eastern platform (as seen from the back passage), which is clearly visible as a distortion of perspective.

Linedef 865 has its lower texture on the wrong side. This creates a slight asymmetry in the floor of the doorframe (sector 149), which has a "step" texture on one edge but apparently overlapping CEIL4_2 textures on the other.

Sidedef 1363 is missing its upper texture. The grid texture on the underside of the door (FLAT20) underscores the resulting rendering anomaly, as the grid appears to roll behind the ceiling of the passage (sector 55).

Linedef 1071 has its upper texture on the wrong side. This is virtually impossible to detect during normal play, because the upper corner of sidedef 1379 cannot be seen after the player has fallen down into secret #9.

Slime trails may appear in the following locations (see screenshots below):
 * Most inner corners of the circular marble hallway.
 * In the lower circular hallway, looking at the central structure from the southwest.
 * As one returns to the exit door from secret #10.

The blockmap bug may be triggered by firing eastward down the long blue corridor.

There are 12 known anomalies in this level's REJECT table.

Demo files

 * [[Media:e2m4secr.lmp|No monsters, 100% secrets walkthrough]] (file info)
 * [[Media:e2m4wik1.lmp|100% kills, items, and secrets on ITYTD]] (file info)
 * [[Media:e2m4wik2.lmp|100% kills, items, and secrets on HNTR]] (file info)
 * [[Media:e2m4wik3.lmp|100% kills, items, and secrets on HMP]] (file info)
 * [[Media:e2m4wik4.lmp|100% kills, items, and secrets on UV]] (file info)

Routes and tricks
In a straight speedrun, the player's first main risk is being cornered or harried at the blue key. Most Compet-n entrants loop around the baron while waiting for the lift, in order to draw pursuing imps under the door and encourage infighting, then rely on luck to clear a path back to the hallway (it is not unheard of for a monster to get stuck to the doortrack during the lift delay). On the other hand, Adam Hegyi has set several records by using the lift delay to re-activate the door himself. In the NM speed style, infighting may of course happen more naturally, as the player is followed into the baron's room by a shower of fireballs.

In general, the population of the blue hallway is sparse enough to dodge at full speed, although some NM players do pick up the shotgun and a blur artifact for self-defense.

To reach the raised square platform in the center of the penultimate room, it has long been obvious that secret #9 is faster than waiting for three sets of stairs to rise. Squeezing past the first cacodemon is difficult, but important in order that other cacodemons do not hear gunfire and move to block the lower end of the staircase. The short detour to the plasma gun nevertheless saves time overall in pushing past the last few monsters, even if not all are killed.

When you click the switch to raise the exit bridge, there is enough time to move directly to the bridge without using the teleporter. Note that if you do so, and step to the door immediately, the second bridge may not rise quite high enough to reach the supercharge shelf. In that case, you can still take the supercharge, but you cannot get credit for the secret. (Modern Tyson recordings do this on purpose in order to teleport back to the baron battle sooner. )

The ratio of monster hit points to ammo in this map is 0.853 (compare MAP02 of Plutonia at 0.814), so the speed of a max run is heavily influenced by punching, infighting, crushers, and drawing monsters together to reduce the time between kills. The agreed route nowadays is as follows. Whether to kill the first sergeant as soon as he appears, or to punch him on the way back to secret #2, is unclear. The sooner you make a noise, the more monsters tend to gather in secret #3 (to be near you while you clear secret #2). However, a cacodemon wandering around in secret #3 can force you to use some caution, whereas you could otherwise dive into a corner and start swinging.
 * Get the berserk pack immediately.
 * Move east to west toward the blue key, clearing each side room. Run all the way to the shotgun, chaingun, and soul sphere because they will come in handy later.
 * Kill the first two barons with your fist. (This supplanted the status quo of combining the crusher and shotgun at the yellow key. )
 * Get the blue armor and clear the lava pool area.
 * Dodge the first cacodemon at the raised square platform as above, go to the exit, and pick up the supercharge.
 * Return to the previous room, attacking barons from behind in the confusion, and proceed until everyone is dead.

These minor optimizations have also been demonstrated: With adept footwork, you can run through the door of secret #5 before it closes.
 * Kill one humanoid while waiting for the square lift to rise. (This even works in Tyson mode! )
 * Where cacodemons and demons appear together, induce infighting and then punch the cacodemon from the side (similar to fighting fast barons on E1M8).
 * Invoke the noclip bug to prevent secret #7 from sealing itself until you are on your way out.   If this should fail, using your fist on the lost souls is faster than the chaingun, but more dangerous as well.
 * Use the chaingun to kill the last two imps, since hitscan attacks can get under the rising door much sooner than plasma.
 * Shoot at the last two imps while backing away along the supercharge bridge.

NM100S runs also tend to proceed east to west through the first part of the map, with the following modifications. To reach the exit without the blue armor is not as daunting as it sounds in this case, because the only monsters encountered afterward are the lost souls in secret #7, the cacodemons on the rising stairs (who can be dodged if you don't shoot), and the three monsters in the exit area (who can easily be pushed aside with plasma). By using the noclip trick, you can even skip the lost souls.
 * Do not fire at the beginning, so that you can eventually collect secret #4 without a battle. Cut a wide arc around the gray column while waiting for the square lift, so that the imps kill the sergeant, whose gun you can grab on the way out to guard against traffic jams (most notably in the chaingun area).
 * At secret #2, weave back and forth as the wall lowers, which seems to cause at least one demon to attack the cacodemon instead of you. The cacodemon will lunge to that side, leaving you just enough space to lean into the secret sector.
 * Respect the fast demons: do not actually try to pick up the supercharge.

In the UV -fast style, many secrets should be entered fully to stock up on ammo, simply because punching monsters is more hazardous than in UV max. The overall ammo shortage, however, still makes it necessary to punch barons and (for example) fight cacodemons with the shotgun at short range; blur artifacts should therefore be avoided as they make the faster projectiles nearly impossible to dodge. Expert players also conserve bullets for close-quarters battles.

With fast monsters, the southern part of the map must be cleared relatively methodically, because the open layout makes it easy to become surrounded. In particular, secret #4 cannot now be collected rapidly, as the nearby monsters would have enough time to reach the nukage pool and cut the player off. On the other hand, such a strategy allows secret #3 to be cleared by punching in the first area, as the incoming fireballs from the west serve to thin out the crowd of demons. The easiest way to cross the crooked catwalk is to run due east toward the radiation suit.

UV -respawn demos are optimized by simply not killing the large monsters, who are so large in this case that the total run can be shorter than the UV max record. Compet-n players have compensated by entering the front areas in roughly the opposite order (blue key, backpack, computer room, secret #3, secret #2) to inflate the number of imps encountered, then re-clearing the computer room on the way to the yellow key.

Because the berserk fist is used so frequently in UV max mode, UV Tyson recordings resemble their armed counterparts more than is usual. According to Drew "stx-Vile" DeVore, it was Radek Pecka who first realized that secrets #7 and #8 could be completely ignored (although of course that gives the player less health to work with). The level has even been completed without the blue armor. Absent a weapon, it turns out to be most efficient to kill the last two imps just before exiting.

The newest UV pacifist runs imitate the UV speed route exactly, relying on luck to wriggle past the imps at the end, but many players detour to the invisibility and armor in the oval nukage river, and/or to the second supercharge, to be on the safe side. The UV speed record may always be slightly faster because the plasma gun is available to press toward the exit switch. However, the bullet into the wall to draw the westernmost imps out of the center of the blue hallway, frequently used in the UV speed style, is far from commonplace among pacifist runners.

Current records
The Compet-n records for the map are:

Inspiration and development
An early version of this level appeared as E1M13 of Doom 0.5, and may also be based on E1M10 of Doom 0.4.

This level was used to record the built-in demo in the very first shareware release of Doom.

Trivia
In single-player mode, this map contains 11 rockets (22 on I'm too young to die and Nightmare!) but no rocket launcher.