Blackout Basement: The "I can't see a thing!" levels, which limit your view to a small circle around the Spelunker, are one of the worst hazards in the game. The remake is even worse; you're given a torch to carry through the level, which illuminates in a much smaller area than the flares did in the classic version. And you're only given one this time. Fortunately, you can light stationary torches on the ground so you can somewhat see your way through the level should you want to backtrack and pick up that damsel you spotted. Certain human enemies will also be carrying torches. If you manage to douse your torch in water, it can be relit from a wall-mounted burning torch.
Boring Yet Practical: Rocks do two (one in the remake) damage per hit, are reusable, are good for triggering traps safely, cannot be destroyed except by lava, and can be thrown a pretty good distance. With a little practice you can destroy most enemies long before they become a threat. The only downside is that you need to be careful not to hit yourself on the rebound.
Bottomless Pits: The third major area of the caves is mostly platforms over a yawning abyss. The remake's death journals show that they're literally bottomless; the player character writes "Help, I'm still falling!"
Chunky Salsa Rule: Falling from the top of the level to the bottom or getting caught in an explosion causes tremendous damage but can be survived if you've got an unnaturally huge amount of health. Getting squished (by a boulder, for example), getting frozen and smashed to pieces, falling onto spikes or into lava, or getting eaten by a man-eating plant, however, kills you instantly no matter how many hit points you've got.
Dungeon Shop: Six different kinds, all run by well-armed elderly men. Rob/vandalize at your own risk.
Equipment-Based Progression: You find equipment and upgrades, but you can also get them by going to a shop or performing a ritual sacrifice. The game is randomly generated, and if you don't find things early, the later levels might be too hard to get through.
Escort Mission: Every time you try to rescue the damsel. Fortunately, she's nearly invulnerable and makes a good human shield (or weapon). You can carry her around. However, in the remake she (or he, or it) is NO longer as durable as she used to be, and can only take a couple of hits before perishing.
Excuse Plot: The plot, like everything else in-game, is randomly generated every time you play.
Fantasy Kitchen Sink: Giant bugs, cavemen, mummies, aliens, ghosts, yetis, Hindu Gods, and more can be found coexisting in the game (with even more added in the remake). Particularly egregious when attempting to find The City of Gold. You have to Find the egyptian Udjat Eye from a treasure chest, locate the Black Market in a Jungle to buy the egyptian Ankh, die next to a Moai statue to get you the Hedjet (Egyptian crown), and then kill either the mummy (in the original) or Anubis (in the remake) to open the City of Gold, which is a primarily Mayincatec legend.
The Goomba: As mentioned above, the snake. All it does is slither slowly back and forth. It is perhaps the only enemy that does not actively respond to your presence or do anything to kill you besides continue its regular movement pattern. It has an Underground Monkey version in the remake called the Cobra, which spits venom in small intervals. It still retains its movement pattern, however.
Unlocking the City of Gold. Unless you decided to look on the game's wiki before playing, you probably won't even know that it exists, let alone the grueling trials required to unlock it.
On a similar note, finding the Worm and the Underworld in the remake. It doesn't help that the second one requires an already excruciating trip to the City of Gold ANDrequires you to defeat the Final Boss in a specific spot that's randomly generated on each playthrough.
The "Wanted Meter." Whenever you rob, attack, or vandalize a shopkeeper's store, all of them aggro against you and a shopkeeper spawns at the exit for the next few levels. How long they stay hostile depends on what crime you committed and, naturally, you're told nothing about this, your only clue being the "Wanted" posters in the shops. However, this system is averted when a shopkeeper dies. In that case, you have to deal with them for the rest of the game.
The eggplant run. To get an eggplant you need to sacrifice a mystery box to Kali. At first glance the Eggplant does nothing except change the music to a sweet retro tune, but there are stories that throwing it at Yama will cause something special to happen. Doing this requires the following; You need to get lucky enough to have a shop with a mystery box spawn in the same level as an altar, then you need to nuke every altar you see until Kali gets angry enough to shackle you with a ball and chain. Next, you need to go the Black Market, and buy/steal the Ankh, you need to get a companion from a slave shop, then you need to use the ball and chain to break through the Moai head without losing the ball and chain. When you get to the temple, you'll need to have your follower carry the eggplant until you're able to get inside of the City Of Gold. There's a good reason the eggplant run is an Urban Legend of Zelda; its extremely luck based and skill dependent requirements means few people have successfully done it.
Inventory Management Puzzle: You'll often have to juggle items and leave some good ones behind, especially with held items. For instance, do you rescue the damsel or keep your shotgun? If you want to do both, where can you leave you shotgun so that it will be safe until you can pick it up again?
Jet Pack: One of the rarest, most expensive, and most useful pieces of equipment in the game. It runs out of fuel fairly quickly when in use, but instantly recharges as soon as you land again.
Ledge Bats: Has been known to happen to players who don't clear out bats before advancing.
Luck-Based Mission: As mentioned in the Unwinnable by Mistake example below, the level generator doesn't always keep up to snuff with path creation. This often results in long, unavoidable falls in certain areas, "dead ends" that force you to spend bombs removing obstacles or ropes to climb over said obstacles, or arrow traps that you have no choice but to get damaged by. Don't have enough hit points? Sorry pal, it's back to square one.
Ludicrous Gibs: Most enemies explode into blobs of blood upon being killed, and some mini-bosses explode into chunks of flesh. And there's a frog that explodes into flames. There is even an item that catches the gibs and gives you health.
Machete Mayhem: Machetes appear as an equippable weapon which asides from having better upside range (at the cost of horizontal range) can also get rid of spider webs.
Man-Eating Plant: Have a taste for player characters, damsels, humanoid enemies, and Shopkeepers. They can't digest the last one though.
Mercy Invincibility: It's there, but it's so short you may not even notice. If you accidentally fall next to an enemy, you will be stunned, and you will die.
Metroidvania: Not a conventional one by any means due to being linear (except the hidden levels), but the way items you collect facilitate (and sometimes are mandatory for) your progress is very reminiscent of the genre. Of course, they are by no means guaranteed to be around when needed.
Money for Nothing: Shops appear less often as you progress through the game, but there is a bonus for hoarding enough money when you beat the game, in the original at least. The remake just gives you points for the global leader-boards, and a Cosmetic Reward for acquiring an obscene sum of money.
Not the Fall That Kills You: Fall damage can be prevented in a number of ways, including falling into Soft Water or spider webs, landing on an enemy, or catching a ledge, not to mention parachutes. However, falling off the screen is possible in Area 3, and that results in instant death.
One-Hit Kill: It doesn't matter how much health you have—Fall onto spikes, and you're done. Same deal with running into Mantraps or the Ghost. This can also apply to bombs, as it's unlikely you'll have enough HP to survive an explosion during a normal playthrough.
Our Vampires Are Different: A particularly challenging foe. It can turn into a bat, jumps higher than any other human enemy, takes more damage to kill than most enemies beforehand and is always hostile to the player.
Perma Death: You die, you have to start again from level one... unless you pay the Tunnel Man to finish the shortcuts or acquire the Ankh from the Black Market.
Personal Space Invader: There are monkeys that will latch onto you. They can throw away your items or stun you. Especially annoying because the vines they are climbing on are mostly over spike pits that kill you instantly, and getting stunned makes you lose grip of the vine.
Randomly Generated Levels: Well, procedurally-generated, to be more precise, but it's certainly randomized enough to keep fresh.
Resurrective Immortality: The Spelunker. It's explained in the remake that the Curse of Olmec prevents anyone who enters the cave from escaping until they defeat him, and if they perish they are immediately revived in the entrance chamber. Which explains why characters are able to write in the journal in such an impossible state to do so (brains fried/shattered/etc.)
Short Range Shotgun: Not a big deal with anything that isn't notably tough — the blast spreads out dramatically and deals a ridiculous amount of damage even at long ranges. Still, don't expect to kill a shopkeeper in one blast unless he's right next to you.
Shout-Out: A few to Indiana Jones. The main player sprite bears a strong resemblance to Indy (other than the red nose). The Gold Idol is a semi-common item. You can get a Crystal Skull during a "restless dead" level. And sometimes the text "I hear snakes... I hate snakes!" appears at the start of a level, which means there's a snake nest in the level.
Shoplift and Die: Prepare to get gunned down if you run out with an item in your hands. Or whip the shopkeeper. Or accidentally throw your unwanted item at him when you only wanted to put it down. Also be prepared to have an alert shopkeeper staking out at the next few level exits. Or for the rest of the game if you happened to kill one. Yeah, they don't mess around.
Shows Damage: Jaws, a giant piranha, gradually loses skin as it takes damage.
Smooch of Victory: Your prize for rescuing a damsel, and it grants you an extra health unit.
Soft Water: That can negate fall damage, but may contain pirahnas.
Songs in the Key of Panic: Hurry music is inverted. The music slows down when running out of time until the ghost appears. In the remake, this is no longer a warning: once the music slows down, it is too late. The ghost appears immediately.
Spikes of Doom: But you can walk through them as long as you don't land in them. Most enemies can be killed by them, too. Later on, there are totem poles that thrust spikes out their sides whenever you come near. The ground spikes are one of several ways a spelunker can die instantly regardless of his health, and the totem poles deal enough damage to kill you instantly if you haven't gotten at least one health boost.
Stuff Blowing Up: Not in the main game itself, but there's a mod for it. This makes the game harder by making every either explode or or on (harmless) fire. This is worth mentioning because how much it changes the game's playstyle by just using this trope. P.S. arrow traps aren't your friends at all.
Then Let Me Be Evil: It has to be admitted, players are probably much more antagonistic than needed to shopkeepers because of how how they pull out their weapon on you. And considering they are most likely just being cautious around somebody who fought their way down, it's almost a self fulfilling prophesy.
Useless Useful Spell: The teleporter. On the one hand, you can teleport four or so tiles in near any direction, and as such can occasionally avoid using bombs to blow open walls. On the other hand, it's possible to teleport inside a wall, killing you instantly. Or in front of an arrow trap. Or into a pit, leading to a death fall.
Video Game Cruelty Potential: The main use for Damsels is to be rescued, which nets you a chaste kiss and a point of health. But they're also surprisingly aerodynamic, making them useful for setting off traps or killing enemies. Even if they die by your ineptitude, they're still valid throwing weapons. They make great sacrifices, too.
One popular strategy for dealing with high-end monsters is to attach a Sticky Bomb to a Damsel and let her dash forward.
The remake allows you to not only be mean to your team-mates but you can even sacrifice them to Kali.
Video Game Cruelty Punishment: Killed a Shopkeeper? Have fun dealing with them as they'll now shoot you on sight and station themselves at level exits for the rest of your current playthrough.
Blew up an Altar? Six Spiders thrown in your face. Blew up an Altar the second time? Ball and chain attached to your foot, which restricts your movement unless you carry the ball (note that you'll be chained to this for the rest of the playthrough). Blew up an Altar the third time? GHOST IMMEDIATELY.
Where the Hell Is Springfield?: The ruins. The intro establishes that they're located in the Middle East, but the architecture is distinctly Mesoamerican, and there are altars to an Indian goddess. The third area's Yeti and ice suggest the Himalayas, but then there's the Moai statue and a volcano at the end, and a number of Egyptian enemies.
And then in the remake you can go to Hell, but the boss is the Chinese depiction of the Asian god Yama.
When All You Have Is a Hammer: Approaching every problem with bombs is effective. Want the treasure in the walls? Bomb them. Want to cut right to the exit? Bomb your way down. Arrow trap in the way and you don't have a rock? Chuck an inactive bomb down and pick it up again. Or just blow it up. Want that statue, but don't want to set off the traps associated? Bomb it off the platform. Wanna rob the shop? See Ballistic Discount up there (hint:it involves bombs). Fighting boss monsters? One hit kill. Final boss? Bombs make it end more quickly.
Inventory Management Puzzle: Averted with the mod Yet Another Spelunky Mod, where you can put mostly everything in your inventory except "big" items like the Damsel, corpses or the Idol.
Made of Iron: You might as well use that damsel you're carrying to set off any arrow traps in your way. She'll be fine.
For the record, the damsel CAN die in the same way that you can, but she's immune to fall damage and take less damage from certain traps.
Metroidvania: As of version 0.99.8, making one of these in the level editor is possible. Several have been completed.
Playable Menu: You take control of the main character as soon as the opening cutscene ends.
Press X to Die: ESC+F1 is the suicide command. It's actually useful for spelunkers attempting to find the City of Gold; once you acquire the Ankh, you have to kill yourself next to a giant Easter Island head in Area 3, and if you want to spare yourself the frustration, ESC+F1 is the easiest way to do it. You can't do that in the remake, though, as the command kills you regardless of whenever you have the Ankh or not.
And Now for Someone Completely Different: You don't play the tutorial as the Spelunker (nor any of the initially unlocked adventurers). Instead, you play as Yang, an Asian explorer who traversed the cave long before you.
Bowdlerise: Attacking a damsel in the kissing booth in the original would make the shopkeeper say "Hey, only I can do that!" and attack you. In the remake, his line has been changed to, "Hey, you can't do that!"
The Cameo: You can rescue Meat Boy from the bowels of the giant worm, and he becomes a playable character afterwards.
Damn You, Muscle Memory: Various changes to how the game game works result in this. You automatically grab ledges now (instead of physically having to hold left or right as you fall) so you can get hung up on ledges more easily, especially with the climbing gloves. There's also the Mantrap enemy; originally you could actually jump on it to kill it if you had a set of spike shoes, but in the remake attempting to jump on it even with spike shoes equipped will result in you getting eaten.
Difficult, But Awesome: The Plasma Cannon. It has horrible recoil (pushes you two blocks away) and it's very easy to kill yourself with it, as its shots do lethal Splash Damage upon impact. But if you learn to utilize it responsibly, you're suddenly unstoppable. It is also the only item in the game which provides you with unlimited environment destruction potential.
Disc One Nuke: Acquiring the Crysknife from a Worm level, which is possible as early as the first Jungle level, allows you mow down most bosses and enemies with impunity.
Eleventh Hour Superpower: In 5-1 you can acquire Vlad's Amulet, which allows you to swim in lava and touch Magma Men without injury. It's limited to Hell and makes the area easier, though the drop in difficulty is less than it would have been if it was available in the earlier Temple.
Everyone Is Bi/Gay Option: All the damsels types (girl, dude and dog) will kiss you, regardless of your adventurer's gender or its own.
Gosh Hornet: The Killer Bee and Queen Bee, complete with their own mini-area in the Jungle.
Haunted Castle: Another bonus area found in the Restless Dead sublevel, in which you can also find Van Helsing, who becomes a playable character when you free him.
Have a Nice Death: The Spelunker often writes in his journal about whatever last killed him, or commenting on how close they were to reaching the next area.
Spelunker: An arrow has pierced one of my vital organs.
Human Popsicle: The mammoths in area 3 can turn you into this. As you could probably guess, getting smashed in this form is a One-Hit Kill.
Infinity–1 Sword: The Scepter and the Plasma Cannon are more powerful than the already fairly Game Breaking Shotgun, but good luck getting either without injury or death! Even if you do manage to get one of those powerful weapons, it's much easier to accidentally kill yourself with both when compared to the Shotgun you can only acquire them late in the game when there are only a few levels left. And if you're going for the City of Gold or Hell, both can only be used for two full levels! By contrast, the Shotgun can be found as early as level 1-1 and can last you the whole game if you're careful!
Infinity+1 Sword: The Crysknife, fashioned out of a giant worm tooth, is found deep within the bowels of a Worm in the remake. You have to go out of your way to get to it, but it essentially One-Hit Kill's almost any enemy in the game, even the more giant ones like the Mammoths in area 3 - and rather than having to be carried, like most weapons, it replaces your whip, leaving your hands free.
Lethal Joke Item: If you manage to get the eggplant to King Yama, throwing it at his head will turn it into a giant eggplant, which does not move or attack and has only one hitpoint.
Luckily My Shield Will Protect Me: The Shield will not only leave you invulnerable to frontal attacks, but you can crush enemies against walls with it. Be careful—you can also crush Damsels and items.
Mythology Gag: The deathmatch theme includes part of the original game's cave theme about halfway into the song.
Power Up Letdown: To anyone familiar with the first game, the Hedjet becomes this. While it still lets you get to the City of Gold, it loses its two other positive qualities from the original (preventing the Ghost from coming and lighting up dark areas without the aid of flares).