MAP30: Icon of Sin (Doom II)

MAP30: Icon of Sin is the thirtieth and final map of Doom II. It was designed by Sandy Petersen and uses the music track "Opening To Hell".

After completing MAP30, the cast of game characters is shown.

Walkthrough
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 spawning endless monsters. It can spawn any monster in the game, with the exceptions of the bosses (the cyberdemon and the spiderdemon) and the different kinds of former humans, who are not demonic in nature. 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 - it may disrupt your rocket attacks (only on harder difficulty levels). 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.

An alternative way to complete this level as been found in which the player can use a hitscan attack. It consists in using the Arch-vile's attack to fly in the air and land on the face of the boss. After, the player needs to aim very accuratly at a certain angle with a hitscan weapon to inflict damage to Romero's head. 

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 provide invulnerability powerups in the slime to ease the task for novices. Monster infighting and some monster telefragging will occur and help to limit how dense the horde becomes. Also, when playing on the skill levels 1 or 2, there are also four invulnerability artifacts at each corner of the pillar.

Official
There are no official secrets in this level.

Non-official
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. 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 spelled by the boss, which is actually a backwards-sounding dialogue that can be spelt as "Oremor nhoj em llik tsum uoy emag eht niw ot". If recorded and played backwards (making it the "correct" playback), it is actually John Romero's voice (distorted and reverted) saying "To win the game you must kill me, John Romero".

Bugs

 * 1) There is a single inaccessible linedef unclosed sector outside the map on the eastern side.
 * 2) 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.
 * 3) 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.
 * 4) A bug or a warning that occurs is that if this level is played on Nightmare Difficulty or with the -respawn parameter set, respawning monsters may telefrag the player if they respawn at the player's exact coordinate at any height of his vertical column.
 * 5) If you remain in this level for a long period of time after being detected by the game's boss, this level will fill up with monsters. If many living monsters fill the level, it can cause a possible crash, due to the nature of the Boss Entity that endlessly spawn its spawn shooter cubes that turn into monsters when reaching any given surfaces. The possible crash occurs when the number of living monsters exceed the limitations.

Routes and tricks
Originally, Compet-n had a "maximum kills" challenge for this level different from UV max, in which the objective was to get the highest percentage of Kills you could. However, in l30-1840.lmp, recorded on July 9, 1996, Kai-Uwe Humpert demonstrated that if you wake up the monster spawner as soon as you teleport into the boss' room, stay on the platform you teleport on, and stand near either one of the southernmost corners of the next highest platform all without firing a shot, you will be out of the sight of every one of the monsters created and they will never wake up. From there, you can wait while the monsters telefrag each other to get as many Kills as you want, potentially by leaving your computer on overnight, and then finish the level after that. Because of this discovery, the "maximum kills" challenge was discontinued the day of the demo's release.

Records
The Compet-n records for the map are: