Please don't list this on a work's page as a trope. Examples can go on the work's YMMV tab.
Nightmare Fuel: Spore
"That's My Lunch" appears to be a harmless adventure about a little girl and her kittens, rabbits, chicks and...one-eyed lizard babies. You get an invitation to the girl's birthday party at "Hugs Valley". You have to escort the girl to the party, while secretly feeding the animals to these two hungry monsters. To do this, you have to distract the girl with things like a butterfly net. Then you have to lure one of the animals into the beast's lair with candy. Eventually, there's none left, and the girl finally reaches the party. She then looks at the player and says that you've just sold your soul to pay for the gifts. And the guys who made Robot Chicken made this!
Other things of note are "UBD" creations, some of the more...obscene creatures, and Roadkill Roadrunner.
Creatures with the Bard Archetype are meant to be fun-loving party-goers. Sounds awesome, right? Then you read the Blocks of Chance, which contain gems like these:
"There is no purpose. There is no value. There is no point. Life is ridiculous."
"The universe is one big joke, and the joke is on us."
"The best we can hope for is entertainment. We'll get along as long as you provide amusement - fighting our wars for us, fixing our worlds, looking for meaning where there is none, and groveling in the dirt to fetch us plants. So keep it up! Just remember that we're laughing all the time."
The first and third blocks seem to imply their search for the meaning of life made them Go Mad from the Revelation. Make of that what you will.
The mission from Galactic Adventures called "It Came From The Sky." The mission is about a spaceship that crashed near a research base on a frozen planet. You see green lumps of skin on the ground from the creature that piloted the spaceship, and you talk to some of the researchers working at the base who tell you that most of the other researchers are either sick or dead. You then discover a trail of the green lumps leading to the sole surviving alien from the spaceship, who tells you that he accidentally made the researchers sick, but one of the researchers' daughters has an immunity to the disease. She follows you and then you discover that the researchers have turned into zombies when you see one of them attack and kill another one. You then have to defend the girl from the zombies as you lead her to an extraction point. The creepiest thing about this mission, however, is probably the music.
The Maxis Adventure called "The Spirits Are Restless." You start out at a town that's been harassed by wild beasts. The mayor asks you to see a druid at the nearby forest. Said druid then tells you that the forest has been corrupted by an Eldritch Abomination, causing the beasts to attack the village. He gives you a staff to go cleanse the shrine where the spirit has taken residence. The only thing standing between you and victory are packs of hostile animals and a creepy forest littered with fog, cobwebs and skeletons. All the while, a music track made of scare chords is playing. This adventure is NOT for the faint of heart. You Have Been Warned.
The soundtrack "Alien Abduction" and the soundtrack "Echoes Underwater", which is even worse.
What you can become, late-game, as a militaristic race. Just imagine it from your victim's point of view: your leaders are cowering in their capital, watching as their planets lose contact one by one. They throw every ship and resource they can trying to stop whatever is destroying their worlds- until the last world between them and the empty patch where there empire was disappears. Then, a single ship burns into the atmosphere, flies to the nearest city, and destroys it within seconds. Then, it moves to the next nearest, and does the same. And it just keeps destroying everything while you're pleading with it and trying to negotiate surrender, while it just ignores you. Then, when it hovers over the last city in your entire empire, all you and what's left of your species can do is look up and watch as it drops that final anti-matter bomb...
All because you had blue spice on your homeworld.
While it just ignores you? Oh no, it doesn't ignore you, it hears your pleas of surrender and laughs in your face as it gleefully annihilates every living thing on your planet in whatever way seems amusing to it this moment. Destroy all the cities in an anti matter explosion? de-terraform the planet into a barren rock? Blow the whole place to a flaming magma ball of uninhabitable mess. Kaiju attacks? And the worst part is the planet being attacked doesn't even get the choice. It is all up to the whims of the captain of that despotic space vessel claiming (or destroying) one more world for The Empire!
And it gets better(worse?), think about how your home planet reacts to everything you do out in the galaxy? They simply let you do whatever you want and do not complain even a little about it. So for those ships running amuck in the galaxy destroying everything? They are doing it with the full support (or worse, the complete apathy) of their leaders in whatever government is in place for them.
Imagine for a second, you are a member of a perfectly peaceful race of herbivores, enjoying your days eating fruit and breeding with lady herbivores. before you have the chance to react a group of carnivores appear out of thin air (sneak skill) and mercilessly slay and devour YOUR ENTIRE SPECIES. Just. Because. They. Could... yeah.
Imagine this: You're a creature that just crawled out of the primordial ooze. All around you are some horrific eldritch abominations. The more scary ones actually being incredibly docile... And then come the 50 foot killer potatoes.
Epics in general. They're bad enough if you're lucky enough to see them from afar, but it's surprisingly easy to not realize you're close to one until it's too late. "What was that roar? Why did a pack member vanish from the list?" You turn around and...
It's even worse if you have the graphics set to high but have a graphics card that can't keep up; occasionally, a creature will take some time to fully render. As a result, you could wander into what looks like an empty field only for an Epic to literally appear out of nowhere in front of you.