Bogey

This monster was originally made by my friend for his campaign. It was supposed to be a sort of constant threat to the party. We fought it 4 times throughout the campaign, and it wasn't even part of the main story, but it felt like it was always there, watching. Each time we fought it, we only barely managed to drive it off, though we thought we killed it on two separate occasions. (We were wrong)

It's a trickster that delights in playing with hope and fear. It may feign death, or flee. In combat, it won't necessarily take the most optimal actions to defeat the party, favoring tricks or dark humor. Outside of combat, it might pick a specific PC to torment, appearing to them alone for weeks to them think they're mad. In our case, one of us had this stone eye item which basically acted like a permanent skrying spell you couldn't turn off. The bogey stole it and would periodically show the player a view of the party from above or some ridiculous angle, letting him know it was watching. Other times it would show him horrible scenes of carnage, having dressed up corpses to look like the party, using its chains to move them around in a macabre puppet show.

It hunts the party like a rakshasha, but it doesn't necessarily want to kill them. It just wants to play. It just so happens that people it plays with tend to wind up dead. It was a lot of fun for us, and I highly suggest you use it in a similar way. 

As with all of my homebrew stuff, if you have any feedback/suggestions you've thought of when using this, please let me know!

The Bogey

There are few who have been known to survive an encounter with one, so descriptions of the bogey are rare. Its vaguely humanoid shape varies depending on the individual, but they're usually described as appearing to be hideously stretched and misshapen with muscles, tendons, and bones straining against its skin in all the wrong places. Its deformed hands curl into savage black claws which it can destroy rock and flesh alike. It runs extremely fast in a horrible lurching motion due to its long, powerful legs. Its face is the stuff of nightmares. A bogey can stretch and deform its jagged mouth to grotesque extremes, though it typically enjoys displaying a mocking grin. Its greedy eyes appear unnaturally wide and reflect light like those of a cat.

While some reports vary, the bogey have been known wrap themselves in long chains with hooks on the ends which it uses to great effect to snare its prey. 

A bogey will mock its victims before killing them. Some would say it plays with its food. It may even feign defeat, playing dead or pretending to be captured, but only as the setup to some terrible joke. Every action it takes is meant to stoke the fear in the hearts of its victims, so their deaths will be all the sweeter. The bogey have even been known to stalk their prey for months, playing various tricks on them periodically until they can never feel at ease. Slow cooking.

The bogey cannot physically speak, though they seem to understand many languages. They sometimes use auditory illusions to "communicate", though they only ever do this as another tactic to spread fear. Their actual mouth can only be used to scream, which is possibly the most terrifying thing a bogey does. Its unearthly scream has been known to turn even the bravest souls.

Sometimes, while stalking its prey it will magically disguise itself. They can take many forms, though each bogey will have its own favorite. Even with this disguise, however, it is often incapable of hiding a wretched grin, as if it can barely contain its laughter.