Alzatho

The Alzatho is a terrifying nocturnal predator spawned from vile necromantic experiments lost to time. Exhibiting a complex parentage that merges dire hyenas, feral swine, and warhorses, these folkloric monsters have established themselves in wastes, sparse forests, and in abandoned spaces and ruins, but never far from civilized areas filled with delicious sentient souls. They prefer humanoid races for their meals, and require sentient food to survive, as they feed directly on the soul energy of the beings they ingest.

They are almost always solitary, though their proliferation throughout the temperate regions of the world suggests that they do mate and propagate at some point in their life cycle; caves filled with crushed bones have been attributed to the Alzatho, but their lairing habits are unknown and presumed to be temporary; they may be entirely nomadic. Few accounts of encounters with more than one individual are known; the danger of getting anywhere near one has limited the amount of accurate information available.

The Alzatho's biology is disturbingly unnatural. The beast is a semi-sentient soul-eater that doesn't settle for merely devouring its prey; it can access their personalities, memories, and voice for months afterwards, as a particularly cruel and effective means of luring still more prey to their doom in its hungry maw. Eventually the soul is entirely absorbed, and barring a greater restoration or similar magic, permanently destroyed. This makes the Alzatho one of the only vectors for truly annihilating those undead and other beings that persist through their souls rather than a physical body, such as demiliches and theoretically, even celestials and greater demons and devils when they are physically present and not mere projections from other planes. An Alzatho is able to ingest any type of sentient creature including humanoids, constructs, fiends and the undead. Those with souls nourish it, and those without are just for its entertainment from killing something.

Though lawful evil in terms of its cunning, the Alzatho is entirely content to devour other evil beings, starting with the softest and most digestible. Its sense of target selection would prefer an evil human to a good Dragonborn.

The process of actually digesting a soul is very little understood, understandably, as those who would have an interest in such power aren't sharing their results, and those of good heart who set off on to plumb such mysteries through close study generally end up eaten long before their conclusions can be published.

The Alzatho's usual, deadly effective hunting tactic is to hang back at the limits of shouts or cries, and use the voice of a person in distress, a child, or other similar voices when pursuing one or more victims. It will try these voices randomly if it has no stored souls known to the victims, but since it has access every memory of all its victims eaten within the past year, it tries to find additional prey that its meals recognize, and uses their voices to lure these creatures to their death with cruel and calculating efficiency as well.

When it speaks with a known voice within 90' of an acquaintance of a digesting soul, the target must pass a DC12 Wisdom Save with disadvantage or find itself compelled to climb directly into the creature's mouth - even if it sees where the voice is coming from and consciously knows or rationally understands that it's hearing the Alzatho and not the person whose voice the creature is using. Once the victim is in the mouth, the Alzatho also has a short-term paralytic saliva to keep its confused prey from getting back out, and it munches contentedly doing automatic critical damage due to the paralysis until swallowing the victim at 0 HP.

The Alzatho can fight fiercely if things don't go so leisurely, and will also use the voices of the souls they have eaten to misdirect and confuse pursuers, but it will never fight to the death if it can avoid it.

For obvious reasons they prefer darkness, and they excel at ambushing confused prey who expect to see a small child they know, but instead are confronted by a massive, thick-necked hyena warthog horse monster with a mouth like a feral hippo. Moreover, though the beast is evidently merely a mimic, and not sentient itself, it has an uncanny knack for persuading and deceiving others into its maw from simple discussion alone, not even needing to invoke its supernatural charms or paralysis - simply calling out in a child’s voice and suggesting a person should climb into the monster's mouth to pull the child free will often do it.

Should things go seriously awry for the Alzatho, it will attempt to flee into nearby darkness and then backtrack to avoid detection, but will often linger just outside of detection range to continue to pursue 'known' prey. It may follow a person back home from the ruins without the person realizing it - or once it eats a child, it will use that information to go to their house and lure the rest of the family out, one by one, over the course of several nights.

The Alzatho’s pineal gland is greatly desired for magic designed to simulate life or to trap souls. It is said by the Carpocratian heretics that ritually eating an Alzatho’s pineal gland will embed the soul of its last victim into the person who eats it, and the two will forever after share one body, as multiple conscious personalities acting in tandem. The Carpocratians have asserted in their heresy trials that they keep domesticated versions of the creatures for use in these foul rituals, but surely those stories are exaggerated.

Spellcasting Alzathos are theoretically possible, as they would know any verbal spell components that a victim knew. However, even the brightest Alzatho has no more than average intelligence on its own, and it's better equipped to take on martial classes rather than to defeat and eat a spellcaster with powers superior to its own suggestions. 

The Alzatho is resistent to psychic damage and entirely immune to any charm, as well as to soul-stealing or other attacks of that nature, as it literally has no single 'self' that can be charmed or dominated; however clairvoyance, message, and other spells of that nature will work inasmuch as the captured souls continue to exist in a transitional state for about a year after the person is eaten. It is difficult, if not impossible, to determine whether or not contact is being controlled by the dead person, or by the Alzatho perfectly mimicking that person. At the DM's discretion, a person restored from an Alzatho after a long period of ingestion may suffer ability score loss, level loss, or other damage representing the partial digestion of the soul.