If you find this idea appealing in the slightest, you should totally check out Reynaldo Madrinan’s blog Bum Rush the Titan. He’s done a lot of work OSR-ifying Castlevania under the Barovania tag.
Most of a Ghost: Typically, a ghost is an incorporeal manifestation of an individual who has died. While such ghosts may or may not have a full recollection of their lives and knowledge of their present state, they are none the less the spiritual residue of a once-living creature.
A “Most of a Ghost” is less than that. They’re usually created on accident by a careless or distracted necromancer, like skin forming on a pot of soup. Superficially, they’re similar to a ghost in that they’re incorporeal creatures shaped in a more or less human fashion. However, they are not a manifestation of any individual, but rather, a collection of scraps from dozens of individuals, mixed with necrotic energies and other mumbo-jumbo. They’re about as real as Velveeta cheese.
Being both incorporeal and unintelligent, Most of a Ghosts are pretty useless. The best you can usually do with them is have them wander around an area like undead scarecrows, warding superstitious peasants away from your manse.
Hey, don’t look at me. Fishermen are gross.
Anyway, these are the births that result from this act of bestiality. Fish-kind’s revenge against the lusts of man. Fuckface Fish are as large as a man, but have delicate bones and hollow organs which allow them to slip effortlessly through spaces that are seemingly impossibly small. They make their way through water pipes to take up residence in our cisterns, wells, and toilets. When they hear the movements of people nearby, they leap out to attack.
Their goal is to eat human dicks, which are their only source of nourishment, and they will happily beat a person to death if that’s what it takes to access our tasty tasty underpants sausage.
If the target is willing to prove that they have a vagina, the Fuckface Fish will gladly leave them alone.
Sisterhood of the Sine Wave: There exists a mystery cult of women mathematicians, which holds that the Sine Wave is not only a beautiful expression of mathematical perfection, but also, that it is the fundamental bedrock of all truth and beauty in the universe. (They are violently opposed to their counterparts in the Cult of the Cosine, but that is neither here nor there).
Like any mystery cult, they have their little rituals and chants, mostly designed to be spiritually fulfilling rather than efficacious or correct. Of particular note, however, are their burial rituals, wherein the head is removed, and anointed with sacred equations. It is then released into the air, to bob up and down with constant forward motion, setting the deceased mind into an eternal contemplation of the beauty of the Sine Wave.
These anointed heads are the very definition of an unstoppable force. As such, the Sisterhood takes great pains with their equations, to set each head in motion on a path which can be followed, unobstructed, for all time. If anything does get in the way of the head’s path, the head will smash through it. This would obviously be injurious to any person who got in the way, but worse yet, could be a true catastrophe if the head were to gradually angle its way downward to plow through the earth.
Despite their stillness, no one would ever confuse these creatures for inanimate objects. It is completely obvious to anyone who looks at them that they’re just waiting for the right moment to spring to life and attack. Yet, despite this complete obviousness it is remarkably difficult to steel one’s self against the inevitable pounce. It always happens during some brief lull in your attentiveness, and they always leap in a slightly different direction than you think they will.
Monkey Kid: Sometimes, human children are born as Monkey kids. Like any birth defect in this primitive time, it is a condition regarded with horror and fear. The child is left out in the wilderness to be eaten by wild beasts, and the parents will be lucky if they are not forever shamed by the community for bringing a tiny monster into the world.
Monkey Kids have small brains, weak spines, and overdeveloped feet. They leap and bounce on all four limbs as they move around, and before Auschuzak, those who survived their infancy lived to a maximum age of about 15 years.
But Auschuzak, Devil Prince of the Yellow Expanse, took a liking to the wretched little things, and adopted their whole race as his children. He extended their lives to that of a normal human, deigned that they could only be percieved by those who already knew they were there, and blessed them with a a purpose.
Once a Monkey Kid reaches maturity (about 4 years old), it will begin to look for a human to latch itself onto. Any human will do, really. Once a suitable target is found, the Monkey Kid will leap onto their back, sink its teeth into their Unhappiness Glands, and begin to feed off their suffering.
The command of Auschuzak prevents the victim from noticing the weight of the creature living on their back, though they may notice how much less pleasant their life has suddenly become.
Twoskulls: A pair of Dragon skulls, one on top of the other. Both are capable of breathing fire, but neither is particularly inclined to do so unless there is some specific reason for it. They’re honestly pretty bored, being largely immobile aside from the ability to spin around, and they much prefer to try and get a bit of good conversation out of intruders.
The top skull is the more talkative of the two. It refuses to acknowledge that the bottom skull exists, referring to the bones beneath it merely as its own “body.” Bodies, of course, don’t have anything of their own to think or to say, and thus, it refuses to acknowledge the bottom skull. The top is arrogant and condescending, but generally pretty friendly.
By contrast, the bottom skull is an unhappy grumbler. It controls the movement, but has a huge inferiority complex about its position rubbing up against the floor. It’s well aware of (and hateful towards) the top skull, and appreciates any gestures of respect show to it.
Firebrain: An oblong skull which flies all around at the speed of sound, and is on fire. They jibber constantly, oscillating between low-voiced, incomprehensible grumbles, to equally incomprehensible screeching. Firebrains are angry, that much is clear. What they’re actually angry about is much less clear.
The real trick of dealing with a Firebrain is figuring out what is bothering it at the moment, using only the few words you can pick out of its speech, and whatever other context clues you can divine from the environment. If a person can appear to empathize with the Firebrain’s plight, they’ll be left alone as a similarly aggrieved comrade.
However, if a passer-by seems apathetic towards the Firebrain’s anger, they’ll be (unsurprisingly), set on fire.