These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
The actual spiders, whose unpredictable jump patterns make them some of the most dangerous enemies in the game.
And cultists who throw you around the same way as yetis. They also jump around very fast. At least they're vulnerable to your whip.
Perhaps the most unexpectedly deadly enemy in video-game history (barring the carp): Frogs. Completely unpredictable jump patterns and timing, inexplicable ability to predict your next movement, and quick vertical movements that make them difficult to take down with the whip. You will die by frog at some point.
Excuse Plot - The plot, like everything else in-game, is randomly generated every time you play.
Game Breaker - Getting a jetpack greatly improves your chances of survival. If you can get a shotgun on top of that...
Then there's the Scepter. Unfortunately, you can't break the game with that indefinitely.
Goddamned Bats - Almost every enemy in the game. There's goddamned spiders, goddamned yetis, goddamned cavemen, goddamned frogs, and so on. Ironically, the bats are among the least annoying enemies due to their slow speed and predictability.
Nightmare Fuel - Spelunky often punishes you for attempting to rush through levels without caution, so naturally, you would think to keep a steady pace, slowly disabling all the traps ahead of you. Everything seems to be going fine... until the music slows down and distorts, and you receive the message "A chill runs down your spine! Let's get out of here!" By that time, this is likely what you're doing. Dawdle around more or take too long trying to find the exit, and the ghost suddenly appears. If it's not enough that it has a tortured, agonized facial expression,◊ it constantly homes in on you, flies through any solid object, and instantly kills you on contact. And when it finally does you in, your body turns to bone and withers away immediately. Also doubles as Paranoia Fuel.
Giant Spiders are also incredibly traumatizing. They're absolutely immense in size, easily double the horizontal size of the player. They wait along the ceiling, sometimes out of sight of the player, and when their prey happens upon the area beneath them, they drop down from the ceiling, which, since you're at level 1, with hardly any Hit Points to spare, you're going to be annihilated. It does 2 hearts of damage, jumps all over the place, and never stops chasing you once provoked. Arachnophobes will have a field day with this thing.
The 2nd area of the game, the Jungle, has the optional boss Giant Pirahna, nicknamed Jaws. It's incredibly fast, homes in on you when you fall into the water in a Rushing Water level, and in general looks terrifying.◊ If that wasn't enough, his flesh constantly decays◊ as you fight him, showing bits of exposed bone matter. Squick.
That One Boss - All of them, but especially the Giant Golden Olmec Head.
The "Kissing Booth" has a red light. This can be easily seen in dark levels.
Hitting the Damsel in the Kissing Booth, accidentally or otherwise, prompts the shopkeeper to say, "Hey! Only I can do that!"
Damsels taken from the Kissing Booth are apparently just as grateful as those rescued from the middle of a monster filled maze. Maybe those shopkeepers aren't such nice guys.
