All There in the Manual - JJ2's plot was only explained in the comics in the manuals, so if you didn't read them you'd have no idea what was going on.
Ascended Extra - Lori, made playable in The Secret Files, started off as a nameless rabbit who Spaz fell in love with at the end of JJ2. She was meant to be his girlfriend, but the game's publisher goofed and called her Jazz and Spaz's long lost sister, killing all romantic intentions. JJ2's ending was never fixed to reflect the change.
Attack Drone: If you free a caged bird, it will follow you around and shoot whenever an enemy is near, but you lose it if you take damage. In the first secret level, you play as one of these birds.
Bewitched Amphibians - In the sequel, there's a witch that turns you into a frog, and being kissed by Eva Earlong turns you back into a hare. There is only one only place where this happens, and it is in the demo levels.
Breaking the Fourth Wall: If the player didn't press any buttons a few seconds, Jazz looked at the screen and called to them. In the first game, he said, "What are you doing?" In JJ2, he was more direct: "Hey! Hey, c'mon! Wake up!"
Dummied Out - Tons in Jazz Jackrabbit 2, due to rushed production. Everything from secret levels (at least three, including two complete levels) to bosses (one complete and only used in a later bonus pack, another with no attacks and a third that's invisible despite having sprites) to minor enemies (some functional, others not) and powerups (Frickin' Laser Shield!). There's a bunch of unused sprites in the animation file, too, including '3D' views a-la the 3D Bonus Stages in JJ 1.
Easier Than Easy - several levels can be completed by holding the "right" and "shoot" buttons, and continually tapping "jump".
That's just in Jazz Jackrabbit 2 though. The first game could actually be quite difficult in the later episodes, and goes right up to Nintendo Hard on the higher difficulty settings.
Eternal Engine - The planets Tubelectric, Letni, Orbitus, Technoir, Dreempipes, Industrius, Deckstar, and the Megairbase and the Twin Battleships. Also the abandoned lab levels in Jazz Jackrabbit 2.
Also, Princess Eva is basically Princess Peach if she were turned into a blue anthropomorphic rabbit.
Fantastic Racism - Devan cites the original fable of "The Tortoise And The Hare" as one of the reasons he's so bent on dominating Carrotus; he hated the hare's smug attitude, so, being the sane and rational reptile that he is, he decides that he's going to invade a planet of rabbits (which, technically, are distinct from hares) that haven't done anything to provoke him.
God Save Us from the Queen - In the comic in JJ 2's manual, the Queen strips Jazz of his newly gained title of Prince and throws him in the dungeon when it turns out that Devan Shell wasn't quite as defeated as everyone thought. She then serves as the game's first boss fight.
Averted with the names of the Hell level files however: "Hell", "Hell2", "Damn", and "Damn2" respectively. Interestingly, the Cold Day level is merely called "Freeze". However, it's unlikely that normal / non-modding players of the game (in an age range where this would matter as well) would be closely browsing the data files anyway.
Mineral Macguffin - The extra-large Diamondus gem from Eva's engagement ring in JJ2. For some reason, Devan needed it to power his time machine so he could erase rabbits from history. (It only makes sense if you read the manual first.)
Ms. Fanservice - Seems to be the main reason that Lori is the third playable character (as opposed to, say, a third brother). Her idle animations suggest that "is a girl" is as far as anyone got with her personality.
Princess Eva Earlong also qualifies for this, given her revealing attire.
No Export for You - Two bonus packs, The Secret Files and Christmas Chronicles, both for Jazz2, are Europe-only releases.
Nostalgia Level - All six levels of Episode 3 in Jazz Jackrabbit 2 are callbacks to the first episode of the first game.
Ominous Latin Chanting - The final world in the first game's first episode - Medivo. The track during the level fits well for both the music and overall atmospheric components. Though part of the shareware content, that accessibility actually helped to increase the level set's popularity, rather than leaving players tired of it. Cue remixes still popping up almost 15 years later and you likely have Notable Original Music as well.
1-Up - Jazz's head in JJ1 and a "1Up" text item in JJ2.
Sdrawkcab Name - Letni = Intel. The planet Letni in fact looks like the inside of a huge computer.
Self-Deprecation - The comic in JJ 1's manual has Sonic appear directly: Jazz is complaining that he wishes life was like video games where all you have to do to beat the bad guy is jump on him, and Sonic is seen in the background saying "Somebody get my lawyers on the phone!"
Also from the JJ 1 comic: A turtle acquaintance of Devan's tells Jazz that they studied martial arts together. Jazz says that he's heard rumors that Devan was trained as a ninja, to which the turtle responds that he wanted to, but there were strict copyright laws regarding ninja turtles.
Single-Biome Planet - In the JJ 1, all of them. In JJ 2, most of the game (besides episode 3, which revisits the first three planets from JJ 1) seems to take place on Carrotus, which would make that game an aversion, though since the game never actually says what planet Jazz is on, the only levels we know for sure are on Carrotus are the first four.
Smooch of Victory: Jazz and Eva share a BIG one at the end of the final episode of the first game.
The last boss of the final episode of Jazz Jackrabbit 1 is an evil gray huge superpowered version of Jazz which you fight on a spaceship. I wonder if that sounds familiar.
The sequel follows up with a returning world having a robotic alien that is painfully simple to defeat riding in a hemispherical machine with a swinging ball on a chain attached to the bottom.
The cheat code "APOGEE"note The shareware developer/publisher Apogee, later known as 3D Realms, was Epic's main competitor at the time. reduces the color palette to 16 colors, reduces the speed by half, and displays the text "apology mode".
Taxonomic Term Confusion - The developers seem to use the terms "rabbit" and "hare" interchangeably when rabbits and hares are actually separate genera in the same family (hares are a single genus; rabbits are several others).
Unwinnable by Mistake: Lori has Jazz' helicopter ears, and a modified version of Spaz' flying kick. Unfortunately, this means she doesn't have either of the boys' superjumps, making certain levels nigh-impossible.
Vaporware - Two different versions of Jazz 3(D). Bonus pack The Secret Files was this for a few years before suddenly appearing (but only in Europe).