A series of video games developed at the turn of the 90s, one of the first to be successful at replicating the side scrolling action of the NES Super Mario Bros. games in MS-DOS (more on that down below). The cartoon style platformers are notable for their pioneering use of EGA graphics and shareware distribution, and because they were some of the first games by id Software (who went on to develop blockbusters like Doom and Quake). Although developed by id, most of the Commander Keen games were published by Apogee Software, an already-established MS-DOS shareware game publisher.
Billy Blaze is an 8-year-old boy genius living in the suburbs of Milwaukee, Wisconsin. Due to his impossibly-high IQ of 314, he has learned to assemble various junk and scrap into wonderous pieces of highly advanced technology, his crowning achievement being constructing a spaceship in his backyard from old soup cans and other household objects, called The Bean-with-Bacon Megarocket. When his parents are out and the babysitter falls asleep, he dons his older brother's Green Bay Packers helmet and becomes Commander Keen, Defender of Earth! As his heroic alter-ego, he must fight both ill-intended aliens and his Arch-Nemesis, Mortimer McMire, an Omnicidal Maniac his own age with an IQ of 315.
The games' development began while the team that would become id Software worked at Softdisk, creating small, rushed games as a special division called Gamer's Edge. John Carmack had perfected a technique for displaying smooth scrolling graphics on the PC, once thought to be possible only on consoles. Using this code, Carmack and Tom Hall took the protagonist from one of coworker John Romero's games, Dangerous Dave, stuck the character in a recreation of the first level of Super Mario Bros. 3, and called it Dangerous Dave in Copyright Infringement. The demo was put on a disk labeled "Run Me" and left on Romero's desk as a practical joke. He was glued to the "prank" for hours, and knew they could make a game of their own with Carmack's code. Tom Hall suggested a game about an 8 year old kid who saves the universe, shareware publisher Apogee told them they would distribute it, and the rest is history.
The series comprises several installments:
- Episode 1: Marooned On Mars (1990): The first part of the Invasion of the Vorticons trilogy. While exploring Mars, Keen discovers that the Vorticons have stolen four key components from his ship, and must journey across the landscape to several cities to retrieve his equipment. Featured the first appearance of Keen's signature pogo stick.
- Episode 2: The Earth Explodes (1990): Keen makes it back to Earth, only to discover that the Vorticon mothership is in orbit, and is planning to fire on eight key cities across the planet. Keen must board the ship to disable each of the eight X-14 Tantalus Ray cannons before they fire. The game featured a Darker and Edgier aesthetic; everything attacked Keen immediately, and there were many more pitfalls and dangerous objects to avoid.
- Episode 3: Keen Must Die! (1990): The final part of the Vorticon trilogy. After disabling the Vorticon mothership, Keen travels to their home planet in search of the mysterious force that had directed them to Earth. The game featured various Vorticon cities and establishments, and allowed players to learn the Galactic alphabet (a heavily-advertised feature that allowed players to go back to the previous installments and decipher various signs in the levels).
- Keen Dreams (1991): A Gaiden Game published by Softdisk, where Keen has a dream in which he sets out to fight Boobus Tuber, the vegetable king. The game's canon status is unknown — most fans consider it to have taken place between episodes 3 and 4. The game featured several features unique to the series, including a lack of Keen's pogo stick, and vegetables being thrown as weapons. It also has new graphics, updated sprites for Keen, and background which became the norm for Episode 4 and onwards.
- Episode 4: Secret of the Oracle (1991): The first part of the Goodbye, Galaxy! two-parter. After finishing a new Faster Than Light radio, Keen discovers a plot by a new alien race, the Shikadi, to destroy the galaxy. He travels to the planet Gnosticus IV to consult the Keepers of the Oracle (an ancient alien race), but discovers they have been captured, and sets out to rescue them. The game featured much larger levels and a wide assortment of enemies, as well as new game mechanics and minigames.
- Episode 5: The Armageddon Machine (1991): The final part of Goodbye, Galaxy! Keen lands on a massive space station called the Omegamatic, manned by the Shikadi, and sets out to deactivate the machine and save the galaxy.
- Episode 6: Aliens Ate My Babysitter! (1992): Keen's babysitter Molly is kidnapped by an alien race named the Bloogs, and he must rescue her by fighting his way through the planet Fribbulus Xax. The game was published by FormGen and resold by Apogee.
- Commander Keen (2001): A Game Boy Color title published by Activision.
Though Aliens Ate My Babysitter! claimed that a third trilogy titled The Universe is Toast! would be released in Christmas of 1992 (via its ending credits), it never saw the light of day. Id moved on to bigger and better things, and eventually declared the series dead. However, Tom Hall (no longer with id) has promised to continue Keen's story if he can acquire the rights. Additionally, a Fan Sequel The Universe Is Toast! trilogy has been released, made from heavily modded versions of episodes 4-6. Fan reactions have been overwhelmingly positive.
Tom Hall has announced a Game Maker titled Worlds of Wander, which will include a Spiritual Successor game to Commander Keen titled Secret Spaceship Club. Its Kickstarter campaign failed; however, Tom has said the team intends to work on it in their spare time anyway.
The first five episodes are available as a low-price bundle on Steam, running in DOSBox. An Updated Re-release of Keen Dreams featuring full-screen and windowed modes, EGA and CGA graphics, Steam achievements, score and time trial leaderboards, and cloud saves, was released on September 30, 2015 and Nintendo Switch in 2019, however, the Steam version has been mysteriously removed from the store. Episode six is currently unavailable on modern systems, as the publisher went under and no one seems to know who owns the rights to the game now.
A free-to-play mobile game was announced at E3 2019. It was to star fraternal twins Billy and Billie, the original Keen's children. While the trailer said it would launch in the summer of 2019, no further announcements have been made since then, and evidence suggests it was quietly cancelled in June 2020.
Commander Keen contains examples of:
- Absurdly Short Level: The second level of the first episode consists of a small warehouse where Keen can collect the pogo stick, and the exit is located at the right; there's a small bonus area with goodies at the top, but it's not much on its own either. This is not only the smallest level in the game, but also in the whole episodic series.
- Acid Pool: Secret of the Oracle has two vats of this in the first level, and they show up sporadically throughout. Glowing green goo variety.
- Acme Products: Acme blueprints in Earth Explodes and Secret of the Oracle.
- Action Bomb: Shikadi Mines in the fifth game; floating explosive cubes that home in on Keen and detonate when close enough (which you have to take advantage of to complete the final level).
- Airborne Mook:
- Skypests (flies) in Secret of the Oracle; you can't shoot them, only crush them with your pogo stick when they land.
- The episode also has Blue Birds, which will fly at Keen to try to kill him; and they're invincible (the stunner only working on them a few seconds).
- Amazing Technicolor Population: Due to EGA graphic limitations, all humans are completely white-skinned. As in WHITE-white. Princess Lindsey is also black (i.e. a realistic dark-skinned shade, instead of #000000), if human-featured fairies can be considered human.
- Ambiguously Brown: Princess Lindsey has much darker skin than the rest of the characters in the games, but her ethnicity remains unknown.
- Ambiguously Jewish: Billy Blaze is heavily implied to be this, given that his grandfather, BJ Blazkowicz, was of Polish-Jewish descent and his surname is derived from the Ashkenazi surname "Berkowicz", so this must be true.
- Apocalypse How:
- Earth Explodes has the villains of the first episode position a planetary destruction ship in orbit over Earth. If you screw up, you get to activate it, which leads to a Non-Standard Game Over.
- If you get a game over in Episode 5, you are rewarded with a scene of the galaxy blowing up as happy music plays in the background.
- Aquatic Mook: The fourth episode has the only underwater level in the game, so its aquatic bestiary makes it stand out: Underwater Mines (self-explanatory), Sprites (white Atlantean-like creatures that shoot energy beams from their tridents), and the massive Dopefish (a large, overgrown green fish capable of eating Keen in one bite).
- Armless Biped: Several of the aliens, including the Yorp and Gargs in the first game.
- Attack Reflector: The Flect in Aliens ate my Babysitter can, as their name suggests, reflect the shots of Keen's neural stunner right back at him.
- Batman Can Breathe in Space: Commander Keen and the Vorticon Guards have no problem breathing on the surface of Mars.
- Big Bad: Mortimer McMire, Keen's school rival, is behind the events of every game but Keen Dreams, which has King Boobus Tuber instead. The Shikadi leader also appears on medium and hard in the final level of episode 5, but isn't the one who set everything off.
- Big Eater: Nearly all of the items are candy, food, or soda. Keen sure loves his junk food. Justified in that he's an eight-year old kid.
- Bilingual Bonus: Though in this case, the language is a "space cypher" used throughout the games.
- Blackout Basement: In Episode 2 Keen can switch off (and back on) the lights in some levels. This is helpful; "A wise Vorticon never jumps in the dark. In fact, even unwise Vorticons will not jump in darkness."
- Body Double: The Mortimer you face at the end of episode 3 is revealed to have been an android clone in the translated letter at the end of episode 5.
- Bond Villain Stupidity: Lampshaded. Keen is surprised that the Gnostic Elders weren't killed instead of just being kidnapped. The council page immediately handwaves this by telling him that the elders are immortal. (Which also excuses for preventing the player accidentally — or not so accidentally — killing them.)
- Bonus Dungeon: Most games have several levels that are not required to be completed. For some, the means of accessing the level are secret and the difficulty level is significantly higher.
- Boss in Mook Clothing: Plenty of them, especially in earlier episodes: The Vorticon that guards the last ship part in the first episode, the Vorticon Elite in each of the Tantalus Ray levels of the second episode, the Vortimoms and Vortininjas in the third episode, and the Shikadis and their dog pets in the fifth episode.
- Boss-Only Level: The final level of the third Episodic Game, as well as the final level in the Gaiden Game Keen Dreams, both consist solely of their respective Final Bosses.
- Bound and Gagged: Molly, whose captivity is further secured by four locked doors (each requiring a different colored gem to open).
- Bread, Eggs, Milk, Squick: The reason Keen doesn't like Mortimer McMire one bit is because the latter (a) taunted him, (b) gave him a wedgie, and (c) tried to destroy the Earth.
- Breakout Character: The Dopefish, who has since made cameos in several games over the following two decades (and counting).
- "Bringer of War" Music: In the last level of the fifth episode, Quantum Explosion Dynamo, an adapted version of Holst's "Mars, Bringer of War" by Bobby Prince plays. This theme was chosen because, in this level, Keen has to disable a superweapon that is capable of obliterating the whole galaxy.
- Brother–Sister Team: Keen's kids Billy and Billie in the abandoned mobile game.
- Brutal Bonus Level: All of the secret levels are on the difficult side, as are most of the optional levels in Earth Explodes. In the case of the Bloogdome from Episode 6, the red hand sign (denoting dangerous optional areas) is visible from the world map, as well as at the entrance of the level.
- The Bully: Mortimer, who enjoyed giving Billy swirlies.
- Burp of Finality: The Dopefish pauses to let out a burp every time it consumes one of the small fish following Keen, which gives Keen a few seconds to swim past the Dopefish. It also does this after eating Keen, but the sound is then muted out by the sound of Keen dying.
- Cain and Abel: Molly, who seems to be a good person by all indications is the Abel to her younger brother Mortimer, who is the Big Bad.
- Canon Discontinuity: Tom Hall's stance on the 2001 Game Boy Color game, and the abandoned 2019 mobile game.
- Can't Move While Being Watched: "Secret of the Oracle" contains an enemy called the Mimrock. It looks just like regular rocks found throughout the game, and as long as Keen is looking in its direction, it remains motionless, but when Keen is looking away it can sneak up and pounce on him. And to make things more difficult, Keen's neural stunner only works on them while they're moving, although they can still be defeated (as long as you're not on a slope or a vertically different platform) by shooting at them then quickly walking in the opposite direction..
- Catapult Nightmare: Keen Dreams was supposed to end with one of these. But due to space limit or time issues, this scene was cut from the game. It can still be seen here.
- Circling Birdies: In games 4-6, any enemy stunned by Keen will have them. If you don't see any Circling Birdies, that means the stunning will wear off in a matter of seconds.
- Continuity Nod: Billy Blaze's full name is William Joseph Blazkowicz II, after his grandfather, who you probably know better as "B.J.". The trailer for the cancelled mobile game also had a shot of some family photos on the wall with B.J. and his daughters from Wolfenstein: Youngblood in them.
- Cool Starship: The Bean-With-Bacon Megarocket. It's made of soup cans and runs on Everclear. Admit it, you want one.
- Copy Protection: Aliens Ate My Babysitter requires you to identify a random enemy by name before you can play it. The enemies are never identified in-game, requiring you to have an instruction manual on-hand.
- Cranium Ride: The series features at least two cranium-rideable creatures — the harmless though annoying red Bounder in Episode 4 and the somewhat hazardous Gik in Episode 6, which Billy can ride, but only when it is upright. If not being ridden, it will jump at Billy and slide upside-down on its shell, with lethal intent. Gik riding allows the player to cross slime puddles easily.
- Cumulonemesis: A cloud-like enemy note appears in Secret of the Oracle. Initially, they look just like the other clouds in the game, but when Keen walks past them, they open their eyes and begin to chase Keen, trying to strike him with lightning. They are immune to Keen's neural stunner, but Keen can easily outrun them and even if they catch up, it takes a few seconds for them to unleash their lightning.
- Cypher Language: The Standard Galactic Alphabet. In many of the episodes, there are samples of text written in this language. In the respective secret levels of Episodes 3 and 6, the translation from the SGA Alphabet to the Latin one is provided.
- Damsel in Distress: Molly in Aliens Ate My Babysitter, who is kidnapped by the aliens of the planet Fribbulus Xax. This was orchestrated from the shadows by her brother Mortimer, Keen's nemesis.
- Damn You, Muscle Memory!:
- Playing games 1-3 vs. 4-6. In 1-3, the spacebar brings up the status dialog (lives, points, ammo, etc.), and to fire your weapon you need to press Ctrl and Alt at the same time. In 4-6, the spacebar (by default) fires your weapon, while the Enter key brings up the status dialog. In the latter games, you can change the weapon-fire controls to the same as 1-3, but you can't change the status dialog key.
- To a lesser extent, in the classic games Alt will toggle a switch if Keen is close to it rather than toggle the pogo stick. This can be a problem in 2 if you try to activate the pogo stick too close to a Tantalus Ray. As the vulnerable part of the Ray is usually too high for an ordinary jump, you usually need to activate the pogo stick to hit it, and in some cases it's very tempting to try and activate the pogo stick near the machine....
- Deadly Dodging: You can dispatch some enemies that attack by jumping at Keen (notably the Mimrocks in Secret of the Oracle, who are otherwise not easy to hit with the neural stunner) by luring them close to the edge of a pit, and jumping yourself out of the way when they strike. They are not hurt by whatever hazard can be found in the pit (spikes, lava, freezing water, boiling tar...) but they can't jump high enough to get out, effectively neutralizing the threat.
- Distressed Dude: The Gnostic Elders (and their janitor) in episode 4. Rescuing them (and optionally the janitor) is the objective of that game.
- Dream Land: Keen Dreams takes places entirely inside a dream world governed by sentient vegetables. The goals is to escape this world by defeating Boobus Tuber.
- Dungeon Bypass:
- Keen can skip the entirety of the mountain level in the third game by going back outside from where he enters and climbing over it. In fact, this is the only way to complete the level.
- You can skip most of the "Isle of Tar" level in the fourth game by using the Impossible Pogo Trick to jump a huge gap. However, this will only work on the easy difficulty setting.
- Earth-Shattering Kaboom: In Earth Explodes, you can activate it yourself. Which ends your game, obviously.
- Edible Collectible: In all games, Keen has a range of 100- to 5000-point bonus items, which usually are made of things like lollipops, soda, pizza, candy bars, gum, etc.
- Eiffel Tower Effect: In The Earth Explodes, eight different major landmarks around the world were used to represent the cities in which they were located (and the threat of that city's impending doom):
- Big Ben – London
- Sphinx – Cairo
- Sydney Opera House – Sydney
- Statue of Liberty – New York
- Eiffel Tower – Paris
- Colosseum – Rome
- St. Basil's Cathedral – Moscow
- White House – Washington
- Eternal Engine: The second episode is set entirely within the Vorticon Mothership, while the fifth installment is set entirely within the titular Armageddon Machine. Both settings feature hazards like beam shooters, fire pistons and hot tiles, as well as evil machines (cannons in the second game, generators in the fifth) that have to be disabled so the titular character succeeds on his mission. Some levels from the third and sixth episodes are mechanical as well, as they're respectively the bases of operations for the Vorticons and the Bloogs.
- Every 10,000 Points: In the Invasion of the Vorticons trilogy, you get an extra life for every 20,000 points.note
- Evil Counterpart: Mortimer McMire, Keen's arch-nemesis, who constantly taunts Keen for having an IQ that's 1 point lower. He also looks quite similar, wearing a black helmet instead of a yellow one.
- Evil Genius: Mortimer McMire, who has an IQ of 315 and wants to destroy the world/galaxy/universe, and is willing to let his sister be kidnapped by human-eating aliens.
- Evil Living Flames: In the fourth episode, living fire monsters (Berkeloids) roam in the Isle of Fire level, throwing fire constantly. They cannot be defeated or even stunned, only avoided.
- Eye on a Stalk: The Martians have these; Yorps have 1 and Gargs have 2.
- Fake Platform: The first game has blocks, often just before a key card, that Keen can fall through but not jump back up through. And in the fifth game, there are platforms which slide in the opposite direction if you approach them.
- Family-Friendly Firearms: A justified case. Keen uses rayguns in the first three episodes, the Invasion of the Vorticons trilogy (and the opening story of Keen Dreams); he then switches to a Neural Stunner for the rest of his adventures. This was due to how all the Vorticons Keen slaughtered were mind-controlled instead of evil and Keen didn't want to risk ending up responsible for the annihilation of an alien race again. Also, stunned enemies with stars circling their heads are more amusing to look at in a game that pioneered DOS as a gaming platform.
- Fan Sequel: While there have been several fan-made games and mods, one specific trilogy has been really well received and adopted as the unofficial "The Universe is Toast!" trilogy: The Keys of Krodacia, Dead in the Desert and Battle of the Brains, three mods of Keen 4-6 with new maps, enemies, and items.
- Final Boss: The Mangling Machine in episode 3 and King Boobus Tuber in Keen Dreams.
- Forgotten Theme Tune Lyrics: "(You've Got To) Eat Your Vegetables", originally released as the background music in several levels from episode 4, was composed with lyrics in the form of Billy arguing with his parents and sister about having to eat his vegetables. The composer, Bobby Prince, explained that this piece was originally made for the vegetable-themed episode Keen Dreams but due to disk capacity constraints the game was released without music. Now it is best known by players as the Dopefish theme song because of its use in the Well of Wishes level.
- Frictionless Ice: There two kinds of ice. One behaves just as you'd expect it would, reducing Keen's traction, but the other is truly frictionless — the only way to change direction on it is by jumping off and turning around.
- Futuristic Pyramid: Secret of the Oracle has four levels (one of them secret) that each take place inside a pyramid. Whether they're new pyramids, or ancient pyramids improved with some modern technology (laser turrets, doors etc.) remains unknown.
- Game Within a Game: In many of the games, the player can play "Paddle Wars" (a Pong clone) on Billy's wrist computer.
- The Goomba:
- The first game has the Yorps, which can't damage you themselves. The only way they can kill you is to push you into something dangerous.
- In Keen 2, there's the Scrub, a similarly harmless enemy. They can actually be helpful as they can be ridden upon to access areas you otherwise couldn't, as they can climb up walls.
- Keen 3 has the Foob, which is a tiny, very shy furball that runs away when approached and dies out of sheer fright when cornered.
- Poison Slugs in the fourth game, which leave behind poisonous green feces that kills Keen if he steps on it.
- The Sparky in Keen 5. It's a black spherical robot that walks back and forth, sometimes charging at Keen similarly to the Gargs in the first game.
- Keen 6 has the Blooglets, which push Keen around like the Yorps in the first game but are faster. They come in four colors and sometimes hold keys of the same color as themselves.
- Goomba Stomp: In Marooned on Mars, you can temporarily stun the Yorp by jumping on them. In Secret of the Oracle, the only way to deal with Skypest insects is wait for them to land, then jump on them with the pogo stick.
- Gravity Is a Harsh Mistress: Episode 6 features an enemy called the Nospike, which can be tricked into charging off a platform if Keen jumps out of the way in time. If so, it will hover in the air for about 2 seconds while a question mark appears above it's head, then it falls to the ground and is stunned (in the same manner as when Keen would have simply shot it).
- The Great Repair: In Marooned on Mars, Keen must find the necessary parts to repair his Bean-with-Bacon Megarocket so he can return to Earth.
- Hard Mode Mook: The Shikadi Master from Keen 5 is the only enemy in all Keen games who is completely absent in easy mode. You only encounter him in normal and hard, with hard even having 2 of them simultaniously.
- Harmless Freezing: Getting hit by an ice cannon from episode 1 encases Keen in a solid block of ice which melts after a few seconds (or if it gets hit by an enemy projectile), after which he's none the worse for wear. note
- Have a Nice Death: The lost-a-life sound effect in episodes 4 through 6. Doubly so if you happen to bounce onto something else dangerous.
- Hijacked by Ganon: The series does this with both major trilogies — it turns out the "Grand Intellect" manipulating the Vorticons is actually Mortimer McMire, Billy Blaze's rival from school. Then it turns out the ruler of the Shikadi, the "Gannalech", is just McMire again (the Shikadi heard "Grand Intellect" but couldn't pronounce it). Also, his babysitter Molly from Aliens Ate My Babysitter turns out to be Mortimer's sister.
- Hint System: In the Game Boy version, arrows appear in the background to give players hints about the surroundings (because the screen is otherwise too small to see whether or not you can make a Leap of Faith).
- The style of the opening credits for Commander Keen: Goodbye Galaxy, is the same as that used in The Terminator, with the letters scrolling and overlapping in the background and eventually zooming out to reveal what they say.
- Letting the demo run eventually takes you to a screen of diagonally scrolling text in the style of the Star Wars opening.
- Idle Animation: In Keen 4–6, Keen takes out a book to read and, in one level of Keen 4, moons the audience. In Keen Dreams, he falls asleep.
- I Fell for Hours:
- A fortress level in Episode 3 (Keen Must Die!), where Keen falls into the deepest basement of what seems to be the storage room for an unlaunched rocket.
- The secret level in Episode 5 (The Armaggedon Machine), where Keen can only access the two main bodies of Korath III Base from the bottom (and since both parts have to be explored, he has to fall there twice).
- Improbably High I.Q.: And how, exactly, do you measure an IQ as high as 315. And how does anyone on Earth have an IQ of 314?
- Infinite 1-Ups:
- The Earth Explodes has a rather egregious example in the Paris Tantalus level, where if you know how, you can get enough points to get more than one life each try, which can theoretically lead to infinite lives and infinite points. At least one level in 3 allows for the same abuse.
- In Marooned on Mars, not only does the secret level allow this, but, since getting to it involves using a teleporter inside another level, you can loot the latter level, teleport out, make your way back on the world map, and repeat, allowing you to gain infinite lives (and ammo) without having to suicide. Said other level also has enough points itself to gain an extra life if you so choose to loot it first.
- The secret level in The Armageddon Machine contains enough Vitalin to gain two lives at the very start. Die, repeat...
- Insufficiently Advanced Alien: The Bloog from Aliens Ate My Babysitter are evidently capable of space travel, yet their most advanced weaponry is a large club.
- Insufferable Genius: Doesn't get much more insufferable than trying to kill everyone who is less intelligent than you.
- Interchangeable Antimatter Keys: Only in Keen Dreams. In all the others, only ONE key will unlock a specific door.
- Invincibility Power-Up: Keen Must Die! has an ankh-shaped relic that makes the eponymous character invincible for a few seconds. They're very useful to dodge dangerous enemies like Vortininjas and Vortimoms.
- Invisible Block: The blocks are at least vaguely visible if you pay attention. In the first game, they have one visible pixel which shows up against a black background, and never appear anywhere except against a black background, thanks to the block and background actually being the same tile; and in the fourth game, they sparkle briefly every few seconds.
- Invincible Minor Minion: In the first trilogy, almost all robotic enemies are impervious to damage, even the ones that can only push you around. In the second, most unkillable enemies are the tough rather than minor ones (such as the Berkeloids and Dopefish in Secret of the Oracle, or Robo Red and Sphereful in The Armaggeddon Machine).
- It's a Wonderful Failure: Getting a Game Over in episode 2 or 5 treats you to a cinematic of the Earth or the Milky Way, respectively, being destroyed. Bonus points to episode 5 for the music which sounds like it's mocking you.
- Jump Physics: Keen is able to jump insanely high on his pogo stick. In Keen 4, he gains the ability to pull himself up a ledge, which he previously couldn't.
- Kid Hero: Keen is 8, and already saving the Earth first, and then the Galaxy. The abandoned mobile game was to feature his son and daugther, whose age was not given but who were obviously still elementary school aged, and as heroic as their father.
- Kids Hate Vegetables: What kicks off the plot of Keen Dreams, as it starts with Keen getting sent to bed without food after refusing his vegetables, and then gets trapped in a dreamworld where kids that refuse their vegetables are enslaved by sentient vegetables.
- Law of 100: Rain Drops in 4, Vitalin in 5, and Viva in 6.
- Legacy Character: In the abandoned mobile game from 2019, Keen has grown up and has two kids of his own, who carry on the mantle of Commander Keen.
- Lethal Lava Land: The level Isle of Fire in the fourth episode. It's not a volcanic island, but instead a regular one that happens to be in a perpetual fire due to some fire-made monsters lurking within (Berkeloids).
- Lightning Bruiser: The Gargs once they start chasing you. Seeing them jump chasms can be extremely disconcerting.
- The Lost Woods: The first four levels in the fourth episode — Border Village, Slug Village, the Perilous Pit and Hillville. They're dense forests consisting of living trees in the background with smiling faces, but they're inoffensive. It is also inhabited by strange creatures like Slugs which poop periodically, aggressive round enemies named Licks which exhale fire, and weird living creatures (Bounders) which are friendly.
- Marathon Level: The Pyramid of the Forbidden in the fourth game is probably the longest level in the series, divided into no fewer than six large sub-areas.
- Mascot Mook: The Dopefish from Secret of the Oracle is iconic enough to be the subject of many Easter Eggs from a wide variety of other games.
- The Maze: The world map in Episode 3 is this. You don't have to complete all 16 of the game's levels to beat the game, but you have to know which ones unlock then necessary teleporters to reach the island that contains the final level. As it turns out, you only need to beat three to clear the game if you know which path to take, the final boss level included in that.
- Meaningless Lives: The series invokes this trope starting with Keen Dreams (episode 3.5), which introduces the ability to save your game anywhere and 1UP ickups to the series. The first three episodes only allowed saving on the map and only gave you extra lives every 20000 points. Being able to save your exact progress anywhere in the second half of the series renders the three methods of getting extra lives meaningless, unless you are trying to play the whole game without saving. For the record, the methods are every 10000*2^N points, a 1UP pickup, and collect-100-for-a-life pickups (the latter being introduced in episode 4).
- Mini-Dungeon: The Sand Yego castle in the fourth game. It's modeled after the pyramid levels, but it's shorter and less complex, and it can be skipped.
- Military Rank Names: Billy Blaze adopts the name Commander Keen for his alter-ego. He doesn't like to be called ''Captain'' Keen.
- Mobile Shrubbery: Commander Keen IV: The Secret of the Oracle has enemies that hide under boulders (much like the Toy Story 2 traffic cones). They're harmless (and well camouflaged) when stationary, but deadly when moving. And they can jump at you as if they're riding pogo sticks!
- Mooks, but no Bosses: Only three levels in the entire series have bosses: The final level in Episode 3 (Mortimer McMire on his Mangling Machine), Episode 5 (Shikadi Master), and Keen Dreams (Boobus Tuber). And only those in 3 and Dreams are faced in a classic boss battle in which they can (and must, if you wish to win the game) be defeated. the Shikadi Master is an Invincible Villain that only appears in the medium and hard difficulty settings, and acts as an additional obstacle (the real goal of the game is to destroy the Omegametic). That said, there are various Boss in Mook Clothing enemies in the series.
- Naturalized Name: "Blaze", according to the manual, is a naturalized form of "Blazkowicz".
- Nintendo Hard: The military installation levels in episode 3 (Fort Cavort, Fort Vorticon, Fort Vorta Bella, "Fort Vox", and Cape Canavorta) are among the most difficult levels in the entire series. They're all optional, however.
- No Ending: Beating The Armageddon Machine gives you a message saying "See you Christmas '92 when Commander Keen returns to battle for the universe! It'll be the biggest Keen ever!" Sadly, this grand finale was never made, and aside from a few fan-made Game Mods, the series still ends on a cliffhanger.
- Non Standard Game Over: In the second game, there are Tantalus Ray Cannons you must destroy in order to save Earth. There are eight of them, but if you press a switch on the side of any of them, a Tantalus Ray shot will destroy the planet and your game is over instantly.
- Not Quite Dead:
- The Arachnut and Blue Birds from Keen IV can be temporarily stunned if you shoot them with your ray gun, but never permanently killed. (Or permanently stunned. After all, the way other enemies "die" in the episodes IV–VI leaves them with stars going around their heads.) The first time you see them suddenly spring back to life is disconcerting, to say the least.
- The Volte-face from Armageddon Machine appears to remain shut down after you shoot it, but regenerates afterwards.
- In Keen Dreams, none of the enemies, except for Boobus Tuber, can be permanently killed. Keen can only temporarily turn them into flowers with the help of special bombs. On the other hand, if you flower-ize them when they're right next to a bottomless pit, they may fall off...
- Ominous Obsidian Ooze: In Episode 4, the Isle of Tar is one of the three islands located in the southeastern Three-Tooth Lake. It has many pits of boiling black tar which kills Keen instantly upon contact, and at one point he has to go through the deepest pit in order to grab a blue gem and climb back alive (by using some weak platforms to avoid falling). The tar makes an appearance in other levels in the episode, but it's not as concerning in them as it is here.
- Omnicidal Maniac: Mortimer McMire. It's not that he wants to kill everybody, he just thinks that nobody dumber than him deserves to live. Of course, he's the smartest being in the universe, so it may as well be as is.
- One-Hit-Point Wonder: Commander Keen takes hits just as well as you'd expect an 8-year-old kid to take.
- Pajama-Clad Hero: in Keen Dreams, fitting enough, Keen spends the entire game dressed in blue pajamas and pink bunny slippers (though he still has his trademark yellow helmet). Averted in the other games.
- The Paralyzer: Your weapon in Episodes 4 through 6. Most enemies stay "stunned" forever, though—or at least until after you exit the level.
- Pickup Hierarchy:
- Primary: Parts stolen from your ship in Invasion of the Vorticons: Marooned on Mars, Boobus Bombs in Keen Dreams, Wetsuit and Council Members in Goodbye, Galaxy: Secret of the Oracle, Grappling Hook and Giant Sandwich in Aliens Ate My Baby Sitter!. You need the Wetsuit in order to rescue one Council Member who's being held prisoner in the Well of Wishes in Secret of the Oracle, Boobus Bombs are the only things that can defeat King Boobus Tuber (the Big Bad of Keen Dreams), and the Grappling Hook and Giant Sandwich are used to scale a cliff and pass by the Grabbiter (map obstacles in Aliens Ate My Baby Sitter!).
- Tertiary: Point items (usually candy and sugary snacks/drinks - all games), Lifewater Drops/Vitalin Flasks (Goodbye, Galaxy series), Vivas (Aliens Ate My Baby Sitter!), Rayguns/Neural Stunners (Invasion of the Vorticons and Goodbye, Galaxy respectively), Flower Powers (Keen Dreams).
- Extra: Lifewater Flask/Keg-O-Vitalin (Goodbye, Galaxy), Queen Viva (Aliens Ate My Baby Sitter!) - usually well hidden, but these each gives you an extra life.
- Plot Coupon: Used in three of the seven episodic games (ship parts in Marooned on Mars, guardians in Secret of the Oracle, and bombs in Keen Dreams). The second and fifth episodes gauge your progression with the destructive machines you disable (Tantalus Ray Cannons in the former, energy sources for the Armaggeddon Machine in the latter), while the remaining two simply avert the trope in every way.
- Point of No Return: In Aliens Ate My Babysitter, although there is a portal in the last room, it only leads back to the second room; the first room is forever inaccessible once you leave it. Better make sure you grab the blue gem key before you do that.
- Post-Defeat Explosion Chain:
- The Mangling Machine at the end of the third game explodes from top to bottom in a series of explosions after being defeated.
- Boobus Tuber, the boss of Keen Dreams, after being hit by 12 bombs explodes in a stream of explosions.
- Press X to Die: In Episode 2, "The Earth Explodes", your goal is to disable the numerous Wave Motion Guns on the alien mothership. Each of these guns has an "on" switch on them. Guess what happens if you press it.
- Punny Name: The Sand Yego level in Secret of the Oracle, a pun on the city of San Diego.
- Pushy Mooks:
- The first game has Butler Robots. All they do is go back and forth on a track pushing you around and making it harder to jump if they're touching you.
- The first game also has Yorps. Little happy green aliens that hop in one direction, easily shoving you around if you don't shoot them or at least hop on them for temporary paralysis.
- Keen Dreams has giant carrots that run around. Be careful or they'll push you into a pit.
- Commander Keen 4 has Bounders, which are giant, sentient, rubber balls that bounce around and will push you where you don't want to go, though skilled players can ride them.
- Puzzle Boss: The Vorticon guarding the everclear in Marooned on Mars. As you're told by a Yorpish oracle, "You cannot kill the Vorticon Commander directly." The solution is to shoot a cable, dropping a giant slab of stone on the Vorticon commander. Ironically it is possible to kill him directly by shooting him over 100 times.
- Ranked by I.Q.: Mortimer McMire brags that his IQ is 315, one point higher than our hero (which is 314 in tribute to Pi).
- Schmuck Bait: The switches on the Tantalus Ray cannons in the second game.
- Sequence Breaking:
- Due to a glitch in the 1.4 version of the fifth game, it's possible to skip to the top of the Omegamatic without destroying the four machines first. If Keen enters a certain doorway in one of the machine levels after being pushed off a pole by a Little Ampton, he will exit the level and warp to the Korath base, a Bonus Level normally reached from the penultimate level. Completing that level will send Keen "back" to the top floor of the Omegamatic, and the two final levels.
- "Crystalus," "The Isle of Tar," and "The Isle of Fire" in the fourth game each feature an optional shortcut that allows you to skip at least one key.
- Sequel Escalation: The Invasion of the Vorticons trilogy had Keen fighting to save the Earth. In Goodbye Galaxy, he saved the galaxy. The third trilogy, had it ever been made, would have had him up against a plot to destroy the entire universe (and the unofficial Fan Sequel does just that).
- Shareware: To be specific, games 1 and 4 were given away for free; the others were sold.
- Shifting Sand Land: In Secret of the Oracle, the north-west section of the World Map consists of a desert. It contains 3 levels, 2 of which are mandatory in order to proceed. Surprisingly, although the same game also features 4 pyramids, they are not located in this area of the map but rather in a forest more to the south.
- Shock and Awe: The Shikadi are capable of electrifying poles, killing Keen if he is currently climbing one. Their dogs are capable of shooting energy barks, and the Shikadi Masters can throw Electrospheres.
- Shoot the Bullet: In episode 1, you are able to shoot down the robot's projectiles with your own raygun, causing both to harmlessly go zap/zot.
- Shout-Out: Several, the most notable ones being To Serve Man, Wolfenstein 3-D (which still had to be produced) and The Hitchhiker's Guide to the Galaxy (the Dopefish is the second dumbest creature in the universe, after all...)
- Sir Cameos-a-Lot: The Dopefish, a creature who has appeared in a grand total of one game: Commander Keen Episode IV: Goodbye Galaxy. (And even then, he only appeared in one level, Well of Wishes.) However, the creature has made cameo appearances in a lot of games, both created by Id (or Id properties) and not.
- Slippy-Slidey Ice World:
- There are multiple icy world levels in Marooned on Mars, on both the North Pole and the South Pole of Mars. They feature blocks of Frictionless Ice that Keen will slide across if he steps on them, and tiles that cause him to keep moving forward even if the player doesn’t tell him to, unless Keen jumps to come to a stop. They also come complete with ice cannons, of all things.
- Secret of the Oracle features an ice setting, though it averts the Slippy Slidey part as Keen can move around just as easily as on any other level.
- The Social Darwinist: Mortimer McMire. He thinks everybody dumber than him (which is everybody in the universe) deserves to die.
- Spikes of Doom: Marooned on Mars has green spikes that move up and down. Later episodes, such as Keen Must Die! and Secret of the Oracle, only have stationary spikes, but they all kill you in one hit, just like everything else dangerous in the series as Commander Keen is a One-Hit-Point Wonder. In Secret of the Oracle, they're especially common in the mountain and pyramid levels.
- Stealth Pun:
- In order to get to a secret level in Episode 4, one must collect 12 worms together. This creates a giant foot that transports you. The fact that these must be "inch" worms is mentioned only in the help file, which even goes so far to say, "Watch where you step, or they'll be afoot!"
- The level-entry texts in the same episode; "Keen disappears into Miragia", "Keen backs into the Pyramid of the Moons", etc.
- Stock Ness Monster: in Episode 3, a Nessie-like creature called Messie can be seen swimming in the seas of Vorticon VI. It is actually possible for Keen to hop on its back and hitch a ride, which is the only (non-cheating) way to reach this episode's Bonus Level.
- Strange Secret Entrance: The aptly-named "Pyramid of the Forbidden" in episode 4, reached by going into the basement of the "Pyramid of the Moons" and coercing twelve inchworms to come together, at which point they form a giant foot which transports Keen.
- Super Drowning Skills: In episode 4, you can't swim on the world map until you get the scuba gear (even though you stay above water). And in episode 3, pools of plain water kill you on contact.
- Super Not-Drowning Skills: In episode 4, Keen can swim indefinitely while exploring the Well of Wishes thanks to the scuba gear.
- Tech-Demo Game: The original trilogy was made to show off the smooth-scrolling graphics engine, which was once thought only to be possible on systems with dedicated scrolling hardware, and was previously used to develop a proof-of-concept game resembling Super Mario Bros. 3 (that was never released). The SMB3 demo was initially pitched to Nintendo in hopes of getting a home computer conversion to be approved, but Nintendo unsurprisingly declined.
- Temporary Platform: In episode 4, clear "mirage" platforms fade in and out of interactable state. In episode 5, there are platforms that periodically flip their orientation 90 degrees so that they can't be used to stand on.
- To Serve Man: Given a coded Shout-Out in episode 6.
- The Trees Have Faces: In "The Secret of the Oracle", the trees in the background of the forest areas have faces.
- Tuckerization: Princess Lindsey, named after a fan who wrote to ID Software. The Berkeloid, named after a fan (surname Berkel) who suggested an enemy made of fire.
- Underground Level: Melon Mines in Keen Dreams and the cave levels of Secret of the Oracle take place underground. Aside from their labyrinthine design, they play similarly to other levels, though in the latter game the cave levels have a bigger population of enemies like Mimrocks (living stones that attack Keen when he's not looking at them), Licks (round creatures that breathe fire), and Blue Birds (dangerous eagles that cannot be killed).
- Under the Sea: In Secret of the Oracle, the Well of Wishes is an underwater level where you can't jump or shoot, only swim. Its waters are home to numerous mines and the one and only Dopefish. Water in other places simply kills you at a touch.
- Unexpected Gameplay Change: "Well of Wishes" in Secret of the Oracle; the level is entirely set under water, which means Keen is wearing the scuba suit, can't use his gun or his pogostick, moves slower than in the other levels, and can now just as easily go up and down as back and forth.
- Unexpected Art Upgrade Moment:
- Invasion of the Vorticons Episode 3: the ending image is the sole detailed image in all of the trilogy: a full-screen high-resolution image of a Vorticon hand holding a photograph of Keen posing with his heroic medal with a now-liberated Vorticon.
- Subverted in Goodbye Galaxy! and Aliens Ate My Babysitter!, and the sequel fan-made "The Universe is Toast!" trilogy, in that the title screens are the only elements to use high-resolution full-screen detailed images. (The story pages only use character icons and small lower-resolution images.) Although this can be played straight if one is coming from playing the original 1990 Vorticon trilogy first.
- Unintentionally Unwinnable: Due to level design goofs or glitches, in some cases it's possible to leave a level without having achieved the objective:
- On Episode 1, it is possible to exit the Vorticon Fortress level without collecting the Everclear (one of the 4 items needed to complete the game) by jumping over the Vorticon to reach the exit.
- One of the city levels in Earth Explodes have this risk. You're supposed to destroy the Tantalus Ray and then leave through the nearby exit, and in most of these levels that's the only option. In one of them, through ignorance or absent-mindedness, you can exit without destroying the ray; and the level can no longer be completed (there isn't even a warp cheat to get you back in there).
- In the "Cave of the Descendants" in episode 4, there's a door with no floor on the other side, so you fall if you walk through. Due to a glitch, you can, if you're fast enough, go back through the door before you fall, whereupon you instantly win the level. But now you can't rescue the elder from that level.
- It's possible to make Keen Dreams unwinnable if you complete every level in the game but don't collect at least 12 Boobus Bombs (the minimum number required to defeat Boobus Tuber). The game won't even let you enter the final level. Hope you have an earlier save.
- Villain: Exit, Stage Left: In the normal ending of episode 5, the Shikadi flee back to their own galaxy. If you break the hidden fuse in the secret stage (only possible on normal or hard mode), their spaceship won't work, and they're arrested by the Korath III police for double-parking.
- Visual Pun:
- If Keen stands on one of the crescent moon symbols in the Pyramid of the Moons, and left idle, his first Idle Animation is to moon the viewer.
- In episodes 4-6, the doors are opened by using the matching colour gemstone — key stones.
- In Secret of the Oracle, to get to a hidden pyramid Keen must let twelve-inch worms gather under him to make a foot.
- The Walls Have Eyes: 6 has a few eyes on the background of some stages, and the final stage involves a part where you have to use giant eyes hanging from the roof by their optic nerves as platforms.
- Wingdinglish: The Standard Galactic Alphabet. A standard substitution cypher, you can look at the conversion table here.
- Word Purée Title: The Defense Tunnels in the fifth game — "Vlook", "Burrh", "Teln" and "Sorra".
- Your Princess Is in Another Castle!: The janitor at the end of the Pyramid of the Forbidden (which is an optional bonus level). He's not part of the Gnostic Elder group despite being dressed as one, so when Keen rescues him, he's disappointed that his errands through the pyramid were in vain.