Na-ieve

Harry paints the large Celtic ritual circle in the middle of the clearing, using a mixture of lead paint, his blood, forcefully taken unicorn blood, crushed fall flowers and rotten rowan berries. Each component had a place.

The paint and his blood, to stabilise and bind the circle to him. The unicorn blood would initiate the process of the Shire Horse's transformation. The crushed fall flowers and rotten berries would further link it all with Samhain.

Once that was done, he glances over at Kali, who was now force-feeding the sacrifices unicorn blood. Their sickly bodies and expression all quickly fade as they miraculously become healthy, the curse of imbibing the blood taking effect.

The act of drinking unicorn blood in itself wasn't cursed, but this was only the case if the substance was willingly given. Since that was not the case, the thirteen people were all in a state of 'unlife', living but not.

Essentially, they were dead, and it was only the magic of the unicorn blood keeping their bodies functioning. They would have to drink increasingly large volumes to retain this state, until eventually even filling their stomachs wouldn't be enough. There was a reason no one had attempted to gain immortality through this method.

Nodding, he walks over to the Shire Horse, a mare that'd miscarried mere days earlier. It too was lapping up a mixture of sugar water and unicorn blood, which wasn't technically dangerous for it, since the cursed blood only cursed sapient beings.

Once it'd had its fill, he drags it over to the centre of the circle, Kali placing the sacrifices around the edge of it. They shivered and squirmed of course, scared of the goat-legged lady, giant snake, and clear dark magic occurring around them. The fact that they'd all been randomly healed was proof enough that something unnatural was occurring.

Harry steps outside the circle and raises his arms high, "Bidh an oidhche a 'tighinn agus bàs a' tuiteam, a 'coimhead ar fearann agus a' stiùireadh ar càirdean! Tha sinn beannaichte a bhith a 'faireachdainn a làthaireachd, a bhith a' faireachdainn a gairm, agus an comas a dhiùltadh gus an tig sinn gu crìch!" he calls out evenly, his mouth contorting unnaturally in order to allow him to vocalise the unfamiliar language.

He knew it well due to what'd happened between him and the Lich, but it was a first he'd spoken it like so. The group could see the sun setting over the street as he continued his rather long chant. The stars above them grew brighter with each word, despite that the darkness of the forest grew more intense.

Still speaking, he steps into the circle with a bat Kali had handed him. He steps in front of the dazed-looking horse and presents the squirming creature, and without a second pause, it bites into it.

Despite having half of its body devoured, the bat yet lives due to the unicorn blood Kali had forced it to drink. This caused it to squirm even as the large horse chewed on it, crunching its bones and organs until it finally swallows.

He retreats outside the circle once more, "Bidh sinn ag iarraidh ort, a Bhean Uasal Bàs, do bheannachadh a thoirt seachad an oidhche seo!"

Harry feels an itch as his magic is pulled from his body, the ritual activating and causing the captives to scream as their bodies begin shrivelling, turning to desiccated husks that fall lifelessly.

Sickening black plumes of smoke erupt from their hollow eyes and mouths, quickly enveloping the horse and removing it from sight. The tug on his magic grows more intense, but an idea strikes Harry, one that'd drastically alter the ritual...

It was stupid, moronic even, but he couldn't help but relent to the temptation. He allowed his magic to be drawn, but he pushed some raw demonic energy into the link too. He could sees the surprise and slight anger on Kali's face as he does this, but he ignores it.

*Thwoom!*

Green fire suddenly explodes, turning the dead husks to ash, before drawing flaming lines as they're sucked to the centre of the circle where the horse should be stood.

*THWOOOM!*

A huge sound erupts, heat washing over the clearing, but the sudden green fireball doesn't burn any of the nearby trees it hits. Instead, they just wither, drained of life and crumbling like sand or ash.

The draw on his magic grows and grows, but he keeps at it. Finally, the sun disappears over the horizon, and as if someone had pressed a switch, he falls backwards, released from the ritual as demonic flames start to shrink.

Kali catches him, but Harry's eyes were solely locked onto the circle, where the smoke was beginning to clear. "It's... Perfect." he grins toothily as he finally sees the creature.

It'd retained its original size, 6ft from its neck. But it'd lost all of its fat, its skin turning gaunt and scaly while emitting a dark smokey residue that had an impossible-to-identify odour. Wispy green energy flowed from its mane, head, body, and its long reptilian tail. Its face was almost bird-like, a mix between snout and beak, with its eyes replaced by fierce glowing green orbs.

Last but not least were the massive, wings on its back, some parts leathery and some scaled, all emitting black smoke and green energy. It turns towards him, a snort as it furls its wings and walks to him, leaving glowing green footsteps in its wake. (Kinda like this but as I described : https://cdna.artstation.com/p/assets/images/images/026/907/618/large/oleg-bulatnikov-.jpg?1590060017 )

Kali's about to retreat with him in her arms but he stops her, reaching a hand out for the creature. It pauses, before pushing its forehead into his palm, allowing him to strike its surprisingly cold skin.

"I'll call you, Nieve." he whispers, loud enough for Kali, Nanthisk, and his new Demonic Thestral to hear in the silent clearing.

"Nieve... Doesn't that mean 'Bright'?" Kali drawls.

"It does," he caresses the strange glowing green mane, "I think it suits her."