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.
Recently, the video on Virus Hunter Island shows what the Virus can do. It's terrifying and disturbing. The virus can infect whole organs and eventually the whole body. Soon, the infected can infect everyone else. The scariest part is that it mentions that the virus can easily make everyone extinct. The creepy music does not help either.
MONSTER. CARNIVAL. ISLAND.
The Jersey Devil. You look for him in an old abandoned house where something is suspiciously shuffling around. It tuns out to be just a raccoon, but then you turn around and see freaky devil staring at you through the window.
Whatever happened in the Bad Future in Time Tangled Island is never explained. But judging from the terrifying damage and the fact your character, now 50 years old, is the sole survivor, something happened.
The main villain of Survival Island is one of the darkest characters in Poptropica history. He hunts humans.
That One Boss: Pretty much every boss could count. However, just mention the name "Mordred" and people will start foaming at the mouth.
Zeus from Mythology Island may qualify. Your speed and health are about the same as his; it's that he has much better attacks to choose from. Your only attack is to fire one lightning bolt at a time. Each does little damage. He, meanwhile can either fire lightning bolts in all directions at once (difficult to avoid but does little damage), use a charged attack with energy balls that track you (more avoidable but more damaging— Also, you can't attack him while he's charging), or tackle you (easiest to avoid, but if he manages to hit you you can go down in one shot).
That One Level: Greg's Twisted Wizard game on Wimpy Wonderland Island. The ogres are fast,attack in numbers, attack from all directions, and you WILL die if your walls aren't strong enough to hold them off while you kill them with lightning. And God help you if your thunderbolts miss even one of them. Oh, did I mention you only have one life, instead of three, which means that if an ogre gets you even once, you have to start over? And if your inner defenses break down, the ogres become even faster than they already are? Have fun.
Snoopy's Piano challenge on Great Pumpkin, the dots fall too far apart, the piano keys are too close together, and when dots are close together they fall in-between the black and white keys, which are stupidly close together, the bar instanly drops all the way if you miss the first dot and Snoopy makes annoying pained expressions if you are losing making the mini-game harder than several boss battles.
Three words: Astro Knights Island. So hard the developers released an official, in game walkthrough for it because it was the Island with the lowest rate of completion.
The ridiculously hard Dryads level on Twisted Thicket. You have to shake the mouse, but it won't scare all of them away. Countless players have tried to shake them off, only to be carried off into the sky repeatedly.
That One Puzzle: The card-flipping puzzle at the end of Astro Knights has kept many from being able to complete the level.
The Scrappy: If comments on Vampire's Curse Island tutorial videos are anything to go by, Christopher isn't very well-liked. Also, almost everyone despises Zeus.
Surprise Difficulty: Just controlling your character can be challenging at times, and several islands require precise platforming, puzzles, and timing.
Unfortunate Name: An example of one of the horrible names you can have is "Lazy Eye." Also "Creepy Gamer."