Dakon

Ancestor of black bloodline. Started out as a lesser demon and stole his way to glory, including the realm he owns. Loves luxury, but hates spending money on anyone, even himself. Potentially mortal in his young days, but pulled a "Good luck I'm behind seven proxies" on death with multiple immortality granting deals. Just like his looks AND riches, his name is stolen too - I was reading a fantasy book several years ago. It was shit. But it had a cool teacher character of the main heroine called Dakon so uh, it stuck to me.

In order to create his Mobian children, Dakon visited Mobius in prehistoric times. He found a poor hedgehog sap, deemed him similar enough to himself and melted him in a puddle of poison. Absorbing the demon-Mobian essence afterwards, the cat some time later birthed a healthy litter of 5 abominations and left them to themselves to wreck havoc and eventually evolve into the likes of Elec.

It was a long way

Demon form: Cat/Scorpio hybrid of minuscule sizes, with maroon fur and neon-blue accents, including a crystalline pincer and blue, often leaking eyes. Lots of eyes. Mouth disappears and appears at will and can stretch to enormous sizes.

Mobian form: Honestly a Mephiles recolour - it's nostalgia, bite me. He's not for use, anyway. Maroon fur, blue crystals and markings. Black scleras, blue irises. White muzzle. Mouth disappears and appears at will and can stretch to enormous sizes.

Blood colour: Black

Bloodline traits: Demons with diamond-shaped markings and black blood. Tiny demon forms of either cat/scorpio/hybrid. If contained for a long time, their inner demon leaks out with the eye colour, opening up temporary visors in its path.

Brief History

First specimens were created millennia ago by Dakon's influence, and they had the form of Mobian  hedgehogs with crystalline spikes, diamond-shaped markings, toxic  abilities and, obviously, black blood and flesh. In modern times, most  common species of black-blooded demon Mobians are still hedgehogs and  cats, but over the millennia there have been demon individuals in most  recognised species on Mobius, with a wide range of powers and looks.

Demon/Mobian forms and genetics

The  demonic form of these Mobians is always a small-sized, cat-like  creature with a tail ending in a scorpion-like, crystalline pincer. They  have the ability to secrete a liquid, sometimes called essence. The  essence is a thick, slightly fluorescent, and very poisonous liquid,  capable of killing a regular Mobian within a minute. It can solidify  into crystals at the demon's will, and it often looks like they can  sprout crystals from under their fur. The demon and Mobian forms can  both materialise visual organs anywhere on their body.

It's important to note that in 99% of the cases, the main eye/essence/crystal colour is the exact same.

Over  the years of course, the black-blooded demon genes got mixed with genes  of other species of demons, angels, mobians and everything else.  Nowadays, a lot of hybrids have demon forms sharing traits of both  species, and many black-blooded Mobians no longer share some traits with  the ancestor. In general, the more traits a Mobian shares with the  ancestor, the more 'pure-blooded' they can be (though it's also not a  necessity, as seen with Blackbow family). Similarly to vampires and  other such supernatural creatures, black-blooded Mobians can sustain  themselves on blood or flesh or souls, but it's not necessary for their  survival, and obviously nowadays is barely practiced. In fact, trying  any of these is ill-advised, as the demon can develop an addiction which  can be very problematic to fight off.

Overflow Condition

The  closer to pure blood a black-blooded demon is, the more likely it is he  or she will eventually suffer from overflow. Trying to sustain yourself  on Mobians can also increase chances of future overflow.

Generally  harmless and non-lethal, overflow is still a very uncomfortable  condition. When a black-blooded Mobian doesn't use his demon abilities  or change into his demon form for a long time, the essence can build up  in his body. Eventually it reaches a critical point, and the divide  between the Mobian and demon forms temporarily becomes blurred. The  afflicted Mobian can't control the essence, and it involuntarily pours  out of orifices. With the essence pouring over the Mobian's body, it can  also open up additional vision organs, and despite the ears and eyes of  the Mobian being clogged up, their senses are enhanced.

The overflow  can last anywhere from a few days to a few months. It doesn't require  hospitalization, but can be very uncomfortable and sometimes painful  (during additional eyes opening up for example). The essence also stains  horribly and is hard to wash out.

Not every black-blooded individual  has to experience overflow in their life, it's only made more possible  by conditions mentioned before.

Examples of black-blooded Mobians

Electrisa

Traits:  cat-like demon form (doesn't use it), eye manifestation (doesn't use it  voluntarily), enhanced senses, notable essence influence

Due to her  Mobian form being permanently damaged by holy magic, the demon form  partially merged with the Mobian form, causing her left eye to appear as  an ever-shifting puddle of essence. It also has a tendency to drip out  of her eyesocket, especially when crying. Despite its looks, it's still a  functional eye - in fact, it's more light-sensitive than Elec's right  eye.

Worth noting is that the event also caused damage to her demon  form, although she doesn't use it. If Elec were to turn into her  cat-like form, it'd appear to have a chunk of its head missing, with  essence pouring out of it in an endless stream.

Haspar Blackbow

Traits: Vision-related powers, multiple optical organs (permanent).

An  example of a hybrid demon, Haspar (and his many siblings) have demon  forms whose looks are related to their other demon ancestor, not Dakon.  They're all monochrome, and definitely don't look like cats. Despite  that, they all have vision-related powers, and although their essence  isn't visible, it'd be green like their eyes. Genetically, they are very  close to Dakon (only 3 generations apart), but at first glance don't  share that many traits with him, and take after their second demon  ancestor instead.