Sandbox / Nightmare Fuel Dungeons And Dragons5th Edition

• Vargouilles are essentially flocks of flying Shrunken Heads that kiss you and, if you aren't quickly healed, turn you into a flying Shrunken Head. Not even you as in all of you, just your head sprouts wings and breaks off. Added to this is the fact that, while sunlight can delay the transformation, the only cure is a level 3 spell, while the Vargouille is low enough a challenge rating that you may only have level 1 spells available when you encounter it.
• Quippers. Imagine really big piranhas that survive in cold water. Now imagine: you're walking by a pool, and then a giant fish with sharp teeth jumps out and devours you in one big gulp. And they can be anywhere. Paranoia Fuel, anyone?
• 5th Edition revamped the Nothic from a rather silly-looking cyclopean lizardman to a wizard who pried too deeply into forbidden matters and is now a sadistic Seer able to just know things about the people it observes — it doesn't even need to read your mind, it just knows. It deals necrotic damage with its gaze attack, which is to say it can make you rot from the inside out just by looking at you. And nobody knows what they're planning...
• Skulks were creepy enough in 3.5th Edition, the descendants of an ancient empire's "untouchables" caste who underwent a ritual to make them truly beyond notice, able to hide from plain sight, move without leaving tracks, and highly resistant to divination magic, all so they could take murderous revenge on the rest of the human race. Then Mordenkainen's Tome of Foes made them humanoids who went soulless from spending too much time in the Shadowfell, leaving them trackless and permanently invisible unless seen in a mirror... though children under the age of 10 can see a Skulk perfectly. As Mordenkainen himself puts it, "Some children have imaginary friends that their parents can't see. Sometimes these invisible friends aren't imaginary."
• The Sorrowsworn are personifications of all the negative feelings of people in the Shadowfell: The Hungry, the Lost, the Angry and the Lonely. The portraits make them look like Mooks, but when you look at the CR, each would be a challenge for lv. 10 players. These things are so miserable that you almost feel sorry of them. But don't worry, you can help them. In fact, they're not giving you a choice...
• Boneclaws are the result of the ritual used to create liches going horribly wrong, creating a freakishly powerful, emaciated creature with Absurdly Sharp Claws. These monsters will latch onto the nearest evil being they can find as a servitor, even if the host does not realise it. Mordenkainen's Tome of Foes provides a horrific example in the form of a boneclaw latching onto a child and acting on their subconscious desires, leading to it murdering people (most likely commoners who stand no chance against a CR 12 monster) the child dislikes.

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