Sidebar: Demons or Extraplanar Beasts?
Let’s look at where they come from.
More powerful than all the gods combined is the entity known as Archaeox (arr-KAY-ox), known as the Primordial Darkness. It is not known what Archaeox was before, or even if there ever was a before, but now it exists as the “god” of both law and chaos, of both creation and destruction, of madness, and of hunger. It continually births godlings and consumes them. The only godling to ever escape is Dvala (goddess of healing, family, and gentle rain), mother to all the gods, and the only child that Archaeox failed to devour.
No plane is infinite except perhaps Archaeox's plane—certainly no one has ever explored all of Pandorum. To human eyes, Pandorum is a place of madness and utter chaos. It is hell, at least in the sense that this is one of the places where damned souls go. Archaeox is as powerful as it is insane, and it has no worshippers—only parasites. Similarly, the creatures that dwell there are immensely powerful, but insane. It is a hell where the demons are more likely to ignore a traveler than they are to attack it. And no demon is constant. Any type of demon can shift into any type of demon at any time (although the probabilities vary).
Many believe that Archaeox is not a god at all, but something else entirely. It is not known whether he can’t hear prayers addressed to him or merely doesn’t care. While no sane person worships Archaeox, there are many that drain him, like ticks on the back of a god.
Anyone can summon creatures of Pandorum, and nearly every evil cult does (and sometimes good churches, very quietly). Travel to our plane causes their forms to stabilize. A lesser summoned Pandorum-beast will never turn into an elder reaver, for example. So, although they are very different from the demons of Zala Vacha in essence, summoning them is very similar in effect.
If you want an idea what Pandorum (one of Duscuro's two hells) might look like, google a video called Metachaos by Alessandro Bavari. But WARNING: while it is technically SFW, it is pretty gosh darn disturbing. Far more uncomfortable than the traditional fire-and-brimstone sort of hell, I think.
As far as unspeakable horrors go, the Gentle Beast is pretty darn cuddly. It's a vaguely Lovecraftian beastie that will stalk around your PCs while going bump in the night. It's a potent psychological threat that's utterly harmless in combat. . . unless you can see in the dark.
Biology and Summoning
Gentle Beasts are one of the nicest things you'll ever meet in Pandorum, and they are terrifying. Appearance-wise, a Gentle Beast looks like a small elephant (the body size of a dog) that stands on spindly, stilt-like, triple-jointed legs that lift them 8' above the ground. Their feet resemble chicken's feet (but no talons). Where their head would be is instead a mass of tentacles. They are slow and not very durable (although they are amazing climbers, and can fit through very small holes). The entire creature is coated in layers of slimy black membranes and shifting tissues that feel like drowned spiderwebs.
Like all Pandorum demon-beasts, it has no senses. No sight, sound, tremorsense, touch, taste, smell, echolocation, or infrared detectors. Instead, it is omniscient. This is balanced by its slug-like intelligence and utter insanity. While it's impossible to hide from it, there is always a decent chance that it will ignore you (unless directly ordered to attack you by the summoner). However, if you attack it, it will defend itself as best it can.
As creatures of the primordial darkness, Gentle Beasts vanish in the morning sun, leaving only a patch of slime and sick earth behind. They must be resummoned every night. However, after the initial summoning and binding, it is a trivial matter to summon them again. The binding ritual, too, is among the simplest of all the demons of Pandorum—the only thing required to bind a Gentle Beast to one's will is a tiny, miniscule piece of the summoner's brain, which is fed to the thing.
During the night, they stalk through the trees and bellow long, warbling hoots that can carry for miles. These otherworldly cries will demoralize and sicken those who are enemies of the summoner. The sickness takes the form of insomnia, the inability to focus on intelligence-based tasks, slow reactions (such as the beginning of combat), persistent tremors of the limbs, nausea/vomiting, and possibly even seizures when stressed (such as combat). This is a fear-based effect.
Gentle Beasts are permanently cloaked in a shroud of local darkness that extends 5'-7' from their bodies. This makes targeting them difficult. However, if the darkness is dispelled or pierced, a much worse threat emerges—the very sight of the Gentle Beasts is enough to drive a mortal creature mad. This is a very powerful effect, and is much more potent than their other abilities. In a mild case, the creature may become shaken for days OR enraged for the until calmed. With repeated exposure (or if susceptible), the person will flee the location and remain terrified of everything forever OR develop a murderous hatred for all living things, starting with his/her former companions. Each path (fear/rage) is equally likely, and totally random.
When it comes to melee combat, they will attack by caressing the foe with their long, mucous-covered tentacles. These caresses will cause creatures of divine origin to physically unravel and be driven insane, but to mortal races they do absolutely nothing (except give your armor an otherworldly stink that, literally, requires divine magic to remove). Gentle Beasts are too stupid to know that their attacks are ineffective, and will continue to attack back unless specifically ordered otherwise by their summoner. But if you don't mind the stink, their attacks are utterly harmless. Truly gentle beasts.
The thing I like the most about Gentle Beasts is the fact that darkvision is actually a terrible handicap against them. In a party of dwarven fighters (who can usually see in the dark) and a human wizard, the proper party member to kill this thing is actually the wizard. It might take him a full minute of stabbing wildly while being molested by tentacles, but he'll bring the thing down eventually. Far better than a dwarf being driven into a murderous rage forever. If everyone in the party is a dwarf, well, at least it's not as bad as a cockatrice.
Aside from terrorizing communities, Gentle Beasts also work well from within an enemy stronghold. PCs will suffer the effects of the Gentle Beasts while the cultists can ignore it, making it impossible for the party to camp near the place for more than a couple of days.
They're very much an atmospheric, horror-based monster. When DMing an encounter with a Gentle Beast, be sure to play up the warbling drones that these things make. They can hoot without inhaling, so their gurgling howls can last for minutes without pause. Their cries are like hot wind blowing through a torn throat. Their hoots are like the lonely cries of some misshapen, creature in blind agony. Like a stillborn baby deer, somehow struggling back to life in the filthy grove where it was abandoned, crying in infinite pain and hatred. The sound of their movements among the dry branches of the forest is a shuffling, twitchy movement, like the painful spasms of a man with a broken leg. The sounds of them up close is a slithery, slurpy chorus of cracks, pops, and snaps as their skin-like membranes slide over each other. Their 'heart' beats once every ten seconds or so, and sounds like a man trying to swallow something large and disgusting, and nearly gagging on it. Only much, much louder.
They're also very much a support monster. If you hear one in the woods, you know that someone summoned it, so they are never just 'wandering monsters'. In fact, they may be there to draw you out into the woods, and even characters who have fought Gentle Beasts before will have to do it, or suffer the effects of the cries. Gentle Beasts will always have support, because they are always part of something bigger, and probably much, much worse than they are.