When it comes to first-person shooters, you just can’t beat Doom. Sure, we’ve seen a ton of innovation in the gaming world in the 25 years since the title’s original release, but no single game has been able to come close to it in terms of popularity or ubiquity. Famously installed on more PCs in 1995 than the then-brand-new OS Windows 95, Doom makes the major players in today’s market look like total flashes in the pan. Very few will remember Fortnite or PUBG years from now, but gamers will still be populating online forums with talk about Id’s seminal shooter for decades to come. Those other games may have merit, but it doesn’t seem like either of them will be surpassing Windows 10’s install base anytime soon.

Though it’s been combed over relentlessly by dedicated fans, there are still a ton of secrets in games bearing the Doom name that casual players aren’t aware. Just about everyone knows how to access all of the hidden areas in E1M1, but the demon-infested world of Doom runs so much deeper than that.

It’s not easy being a green space marine, but, armed with an arsenal of crudely-rendered sci-fi weaponry, the armies of the underworld won’t stand much of a chance. Plus, with a little extra know-how, the pixelated hallways of the UAC’s martian colonies will prove to be more than navigable—just be sure to stock up on BFG ammo.

30 Yeah, You Can Time Travel Back To ‘92 

Wolfenstein in Doom II
via: dennisasp.dk

Industrial Zone—the fifteenth map available in Doom II’s campaign—harbors a secret which fans of Wolfenstein 3D, a precursor to Doom, will love. Players who managed to stumble upon the level’s secret exit will be taken to one of the few secret levels available in the game. This one, however, is notable for its direct homage to Wolf 3D. Textured and organized very similarly to Id’s previous title, Map 31—or Wolfenstein, as it’s more popularly known—is a shockingly detailed conversion of the original game into Doom’s engine. Id even took the time to implement the famous German enemy sprites.

29 Doom 2016 A Candy Crush Clone In It?

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Doom games are well-known for their excessive nature and relentless action, but 2016’s series reboot introduced a new method of demon slaying. If the player accesses a seemingly innocuous terminal situated near the end of the Lazarus Labs level, they will be presented with a pretty tongue-in-cheek Doom themed version of Candy Crush. Well, it doesn’t have to be Candy Crush, per se, as it plays similarly to pretty much any match-three-tile game out there. It’s a fun distraction, though, and there’s even an in-game achievement in it for you!

28 When Doom Makes Fun Of Itself

Doom 2016 Super Turbo Turkey Puncher
via: youtube.com

Remember that weird little arcade game from Doom 3? A clicker game before the concept existed, the goal of Doom 3’s game-within-a-game Super Turbo Turkey Puncher 3 was—you guessed it—to punch turkeys. Though it couldn’t possibly have held anyone’s attention for more than a few seconds, Bethesda saw fit to include a lone Turkey Puncher arcade cabinet in Doom 2016’s Advanced Research Complex. Bullheaded players may have breezed right by the machine, but dedicated turkey terminators managed to sniff it out.

27 You Can Make The Demons Fight Eachother

Doom Monster Infighting
via: youtube.com

If you’re finding the hoards of the underworld to be a bit too challenging late in the game, there’s a pretty good chance that you could trick some enemies into fighting each other. Monster infighting is a stable of most Doom games, and it can be extremely helpful to those low on health or ammo. Sometimes, if an imp or zombified soldier take a fireball to the back, they’ll likely pinwheel around and return fire regardless of demonic allegiance. There is a demon hierarchy, however, as some lesser-beings know better than to pick fights with tougher opponents.

26 Secret Stage In Doom 2016

Doom 2016 Retro Levels
via: shacknews.com

 This isn’t exactly a major secret given that 2016’s Doom reimagining has been out for over two years at this point, but explorative players have come across old-school, 2.5D original Doom maps scattered throughout the game. Much akin to the dream sequences available in 2014’s Wolfenstein: The New Order which transported the player to a world very much reminiscent of 1992’s Wolfenstein 3D, Doom 2016 allows players to step back through time and briefly pay homage to the roots of the FPS genre.

25 Hacking The Original For EASY Mode

Doom E1M1
via: youtube.com

Doom is pretty well known for foregoing the traditional easy through hard difficulty modes in favor of instituting some more memorable game-mode monikers. From “I’m too young to” the easiest setting, to “Ultra-nightmare,” the game’s most merciless mode, Id did more than implement standard difficulty barriers. However, in the vanilla version of the original Doom, it was possible to set the game’s difficulty ceiling to zero, which meant that no enemies would spawn at all. For those looking to speedrun the game, this may be a pretty solid option, provided that you aren’t a fan of having fun.

24 The Soul Cube Is Back

Doom 2016 Soul Cube
via: youtube.com

Doom 3 players will likely remember the Soul Cube, which was an incredibly unique late-game weapon which allowed players to literally steal health from their enemies. It was slightly creepy, and it would actually whisper “use us” when charged and ready to be deployed, but that hardly hinders what was probably one of the most useful weapons in the game aside from the BFG. Though it can’t be picked up, this disturbing artifact can actually be found in Doom 2016, and it’s actually hidden in the same room as the Demon Destruction minigame.

23 The Terrifying Doom 3 Mirror Secret

Doom 3 Restroom Mirror
via: reddit.com

Another already infamous secret, Doom 3 put players on edge early as a seemingly nondescript bathroom found early on in the game played host to a tremendously terrifying trick. Located in an area not far from the room in which the player encounters the first zombified enemy, there isn’t really a purpose to this room other than the jumpscare it contains. Staring at the mirror for a few seconds will cause the screen will turn red and the camera to zoom in on the Doom Marine’s face as it quickly appears to melt off. Spooky stuff.

22 Get The Super Shotgun In Doom 2016

Doom 2016 Super Shotgun
via: artstation.com

Though it will likely land in the hands of the player at some point during Doom 2016’s lengthy single-player campaign, the super shotgun can actually be located in the Argent Energy Tower in the room in which Olivia Pierce and the Argent Accumulator are encountered. Since the super shotgun—which is a nod to the weapon of the same name introduced in Doom II—shares an ammo pool with the regular combat shotgun, you’ll likely just stick with the more powerful of the two. This new, double-barreled weapon packs quite a punch, and it’s likely to widen the eyes of any hardcore Doom fan.

21 Programming Error In Your Favor — Collect 20 Health

Doom Shocked Face
It can also be seen on a magazine in Doom 3 - via: doom.wikia.com

Anyone who spent too much time playing the original Doom title as a kid likely still has the visage of the Doom Marine emblazoned into their memory. Much like B.J. Blaskowitz, the extremely pixelated hero of Wolfenstein 3D, Doom displays the protagonists’ face at all times in a small box contained within the games HUD. While a depiction of a character’s reaction to certain in-game events was a neat inclusion, a very rare expression of shock could be triggered if the player managed to gain 20 or more health while simultaneously sustaining damage; the event’s rarity the result of a slight programming error.

20 "Glories" Change Depending On Where You Stand

Doom Glory Kills
via: youtube.com

Doom 2016 introduced a unique feature in which defeated enemies could be brought to a gruesome end and return some health to the player. Referred to in-game as glory, the animation which accompanied these ruthless maneuvers were various and detailed. In fact, animations were often dictated by the location in which the player stood relative to the enemy, so taking out an imp from behind would trigger a different animation than attacking him from the front. While a small detail, it helps to reduce the mechanic’s tedium.

19 A Letter From The Demons In Doom 3

Doom 3 Demons
via: kotaku.com

Though the first two Doom titles barely included enough text to fill the back of a shampoo bottle, 2004’s Doom 3 was pretty wordy. While disinterested players could easily skip over the endless mountains of emails and PDA entries hidden throughout the game, inquisitive players could pick up on a particularly strange message saved on a terminal in the CPU Transfer Bay Entrance. This weird piece of text was apparently sent by one of the game’s demonic enemies, and it offered an account of proper sacrificial etiquette.

18 A Secret Nine Inch Nails Reference

Doom Nine Inch Nails Secret
via: youtube.com

In the first mission of the fourth episode in Doom II, crafty players noticed that Id managed to sneak in a not-so-subtle reference to one of their favorite metal bands. In a room not far from the area in which the player spawns, if the player faces the sprite and hits the interaction key, a metal wall directly behind the player will sink into the ground. In its place, a glowing red logo for industrial metal band Nine Inch Nails will be visible. Trent Reznor, the man behind the musical project, has actually gone on to compose tunes for various video games in recent years, which means that this small Easter egg has, in a way, come around full circle.

17 Midi Metal Buried In The Games

Doom Steam Card Exchange
via: steamcardexchange.net

Heavy Metal was the only truly appropriate genre of music to incorporate into Doom’s soundtrack. Some have said that the ambient, eerie tracks found in Doom 64 are a better fit, but how could anyone possibly battle the vicious hoards of the underworld without some rocking tunes. Given that CD-quality audio wasn’t an option when the game first released, the original Doom came packaged with a bunch of midi homages to rock n’ roll icons. In fact, fans have pointed out that Id have more or less directly copied tracks from Alice in Chains, Black Sabbath, and Pantera and added them into their game.

16 Ditch The Weapon Wheel

Doom 2016 Weapon Wheel
via: medium.com

This may have been patched in the months and years since 2016’s Doom reimagining released, but skilled players noticed that the game allowed for an exploit to swap weapons more efficiently. While the ability to carry an entire arsenal of weaponry is great, console players will likely find the game’s weapon wheel to be a bit too cumbersome and slow after a while. However, if the player hits the button to bring up the wheel and points the right analog stick in the direction of the weapon they want quickly enough, the Doom Marine will swap weapons before the wheel even appears on screen.

15 Doom II's Secret (Famous) Pickup

Doom 2 Chainsaw
via: youtube.com

This is already a fairly well-known piece of trivia, but there’s a secret chainsaw pickup in the first mission of Doom II that first-time players are likely to miss. As soon as the player spawns in and is greeted with a sinister-looking entryway populated by two zombified marines, if the player turns left and heads into a small alcove hidden in the side of the room, they’ll come across a chainsaw. While effectively nothing more than a showy melee weapon, Doom II’s chainsaw is an iconic piece of video game weaponry, and new players will probably be eager to get their hands on it as soon as possible.

14 Your True Enemy

Doom II Icon of Sin
via: doom.wikia.com

Another well-known tidbit of Doom information, the Icon of Sin—the monstrous, wall-mounted skull which serves as the final boss in Doom II—isn’t actually the final boss. Though it certainly looks intimidating, if the player activates no clip and passes through the wall on which the Icon of Sin is bound, they’ll actually come across a cheeky reference to the game’s development team. The head of John Romero, Id’s rockstar game designer and co-founder, can be found skewered on a pole in a small corridor. This is actually the sprite the player is intended to hit in order to bring down the boss, indicating that John Romero is a boss both in real life and in the world of Doom.

13 22 Years Later — It Burns

Doom 2016 Icon of Sin
via: youtube.com

The Icon of Sin can actually be found in Doom 2016, though he’s a shell of his former self. He can’t actually damage the player and doesn’t pose much of a threat at all, but he’s actually harboring a subtle nod to the game in which he debuted. Should the player shoot this would-be boss, he’ll actually spout the same reversed line of dialogue he did when he was first encountered in Doom II. Reversing the audio reveals the line to be the pitch-shifted voice of John Romero saying “to win the game, you must [end] me, John Romero.”

12 Shieldbreaker Hidden Technique

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As anyone still playing Call of Duty: WWII’s multiplayer may attest, enemies bearing shields can be really, really annoying. In Doom 2016, shielded enemies may provide a bit of variety and force the player to think on their feet, they are nonetheless more than a little irksome, especially if they manage to bring a particularly gruesome spree of destruction to an unceremonious end. However, the Doom Marine is an athlete with the skills to match Olympians, and these slow-to-react demons usually can’t keep up with him. If the player jumps straight over a shielded enemy, they won’t turn around right away, and Doom Guy will be able to sneak in a few free shots.

11 Procrastinator Achievement

Doom 3 Super Turbo Turkey Puncher
via: youtube.com

Doom 3’s Turbo Turkey Puncher 3 may seem like a silly little time-waster, but those determined to set a high score found that, should the player accumulate at least 25,000 in a single session of the avian assault minigame, their PDA will receive a snarky email congratulating them on their achievement. The email also recognized the player as a shining example of humanity for punching turkeys and informs them that their procrastination will cost them two days of leave. Please stop messing around and get back to kicking demon butt.