Yeth hound

A yeth hound was an intelligent outsider that hunted during night.

Description
A yeth hound looked like a big grey hound with glowing cherry-red eyes and night-black fur. In darkness, only their eyes could be seen. They had very flexible necks with a human like head on it and smelled of smoke.

Personality
Yeth hound packs had a mental need for a pack master. Should their pack master die, they tried to gain a new one, usually a representative of evil like a vampire, hag or necromancer.

Phobia
Yeth hounds feared the sun and never went under sunlight. "Never" was meant literally; if they had a choice between going out under the sun and surviving, or staying out of sunlight and dying, they chose the latter, they were also willing to abandon an advantageous hunt to evade sunlight.

Sunlight had an actual detrimental effect on them. When they were caught by sunlight, yeth hounds were forcefully transported to the Ethereal plane, to be precise to the Deep Ethereal. At night, they returned to the Border Ethereal but were in state in which they could move but not affect anything or be affected by anything. This state persisted until they reunited with their master or a pack member of theirs, something they tried to do as fast as possible.

Abilities
Yeth hounds had good senses, sight, and hearing but their sense of smell was especially good. They were better at tracking prey by smell than other indicators.

They could run faster than humans and were good flyers who could fly even faster, despite having no wings. They glided a bit above ground to hunt and could stop and resume flying with ease and they never grew exhausted.

It was difficult to hurt a yeth hound with physical attacks. Only non-magical and/or silver weapons could hurt a yeth hound, other weapons simply passed through the body of the yeth hound.

Their most special ability however was their voice. When a yeth hound barked or howled, those who weren't evil outsiders in a 300 ft. (91.44 m) radius were filled with an irrational fear that made them run away from the barking yeth hound. A yeth hound used this chance to pursue the fleeing target and was happy when it had such a chance. Yeth hounds were immune to the emotion of fear.

Combat
Yeth hounds fought by biting their enemy. Their bites were aligned to evil and once bitten their enemy was in danger of being tripped by them without being able to properly react to it.

Society
Yeth hounds were one of the servitors of the drow deity Vhaeraun, whose realm was Ellaniath. Yeth hounds were also known to serve Eshowdow of Chult.

When not found alone or in a pair, they organized themselves in small packs consisting of several to a dozen members.

Suitably powerful fey could create them. Once created, they were given as a gift or reward to a person of the fey's choice. The receiver was often assigned the position of pack master of the newly created yeth hound pack and could direct the pack via telepathy, which worked as long as both the master and the hounds were on the same plane.

As mentioned above, yeth hounds hunted at night.

They couldn't speak but could understand Infernal, Common, Elvish and Sylvan.

Background
The yeth hound is based on the yeth hound of the folklore of Devon, a headless black dog known for its wailing.