- This level occupies the map slot MAP30. For other maps which occupy this slot, see Category:MAP30.Template:Doom II 21-30
After completing MAP30, the cast of game characters is shown.
Pick up the weapons and powerups and go through the teleporter (A). The player will arrive at the lowest of a series of large step-like platforms (B). The Icon of Sin will make its unholy introductory speech, and then immediately begin firing cubes with skulls on their sides, which spawn monsters when they land. The Icon of Sin can spawn any monster in the game except for former humans, Wolfenstein SS, Cyberdemons or Spiderdemons. Each 'step' in the simple construction is an elevator which can be activated by pressing on the demonic face on its side. Be ready to defeat or bypass the first monsters created by the boss, and be careful with the incoming cubes, as they may telefrag the player, independent of whether or not he is invincible by means of the God Mode cheat or invulnerable by means of the invulnerability artifact. Get to the top step and use the demonic switch found there. A small platform in the blood pool at the bottom of the steps will rise up (C).
Before you head up, if you are playing this level using the Ultra-Violence difficulty, kill the revenant on the platform immediately below the boss - it may disrupt your rocket attacks. When the pillar-like platform in the slime has stopped rising, press on its side. The square pillar will lower down to the floor (a lift). Stand on the pillar and select the rocket launcher (D). Turn to face the huge cybernetic face of the boss on the wall over the platform across the series of steps. The platform will rise; slightly before the elevator reaches the top, launch a rocket towards the demon's exposed brain. If timed correctly, the rocket will enter the opening exposing the brain (E) and an echoing low-pitched pain sound will be heard. This takes practice to time correctly, although it can be said that firing as the tip of the rocket launcher reaches the gigantic demon's chin is reliable. Three direct hits are generally necessary to defeat the boss. When defeated, explosions occur in front of its hideous visage and the game exits to the intermission screen.
Advanced techniques to destroy the boss quickly include running down to the rising pillar from the switch atop the huge steps, lowering the pillar from the edge once it has reached the top to fire again, and firing while jumping off the pillar, possibly towards the platform below the face to acquire some powerups.
Dodging the horde of monsters spawned by the boss is a challenge, and often one must lure a group of monsters away from the platform before jumping on it again, or kill them with the BFG or another high powered weapon. Arch-viles, pain elementals, arachnotrons, and revenants are particularly disruptive as their advanced attack modes can easily hinder or damage the vulnerable player atop the pillar. Pain elementals and arch-viles should be focused on if the player takes on the horde, as the pain elemental's ability to spawn endless lost souls and the arch-vile's ability to resurrect slain demons are even more dangerous than usual when combined with the endless stream of demons created by the Icon of Sin.
Two radiation suits are located on the platform directly below the evil visage. These are a convenience against the damaging slime at the foot of the pillar, although lower skill levels (I'm Too Young To Die and Hey, Not Too Rough) provides invulnerability powerups, one at each corner of the pillar, to ease the task for novices. Monster infighting and some monster telefragging will occur and help to limit how dense the horde becomes.
If you remain in this level for too long, it will fill up with monsters. With this, there is a possible chance that the game may crash, either due to too many monsters onscreen at once, or an excessive amount of movement by monsters, typically if this level is played with the fast monsters parameter set.
There are no official secrets in this level.
Using the idclip cheat code to pass into the head of the final boss reveals the violently severed head of John Romero, impaled on a spike. This is unreachable by normal means and does not register as a secret, but can be considered an easter egg (it can be reached by being hit by an Arch-Ville from the rear, while jumping forward from the top of the pillar. This will launch the player directly forward with large momentum, throwing him into the forehead gap). Shooting it also ends the level. A side note to this Romero-on-a-stick, when the player enters the main battlefield, he/she is greeted with an arcane chant recited by the boss. If recorded and played backwards (making it the "correct" playback), it is actually John Romero's voice (distorted and reversed) saying "To win the game you must kill me, John Romero". The easter egg was created as an in-joke by artists as explained by John Romero in this video.
- There is a single inaccessible linedef unclosed sector outside the map on the eastern side.
- The linedefs that make up the right side (his right) of the Icon of Sin's face are 264 map units long. However, the textures are only 256 pixels wide, which causes all three of them to repeat 8 map units across from the center of the face. The most noticeable effect of this is that the right horn is separated from the Icon's head. The linedefs which represent the left side of the face are 256 map units long, and thus do not exhibit this error.
- The textures used for the middle of the face feature a dark brown background behind the face, whereas the textures used for the horns feature a black background. They can be seen to clash under the left horn.
- Playing this level for too long without killing the spawning monsters may cause a crash due to an excessive number of monsters in game at once.
- In the same conditions, savegames created on this level cause crash at loading (original Doom only).
- Due to a quirk in the room's design, it is possible to stand on the opening to the boss's weak point. This can only be done via an Arch-vile jump at a specific angle.
- If the player launches a rocket just before dying, and the rocket successfully kills the boss, the dead player will still win the game.
- An older version of Opening to Hell was used as Doom's intro before the current version was used.
- The wall of the teleporter has scary faces gurning at you, an example of the game's satanic imagery.
Routes and tricks
The Compet-n records for the map are:
|NM speed||00:30||Adam Hegyi||1999-06-19||Template:Competnftp|
|UV max||00:30||Adam Hegyi||1999-03-09||Template:Competnftp|
|UV -fast||00:30||Ian Sabourin||2001-12-27||Template:Competnftp|
|UV -respawn||00:30||Marijo "Sedlo" Sedlic||2002-02-23||Template:Competnftp|
|Monsters||ITYTD and HNTR||HMP||UV and NM|
|Powerups||ITYTD and HNTR||HMP||UV and NM|
|Weapons||ITYTD and HNTR||HMP||UV and NM|
|Ammunition||ITYTD and HNTR||HMP||UV and NM|