YCH for  Sylvermor

One day, Jack was hired to perform a fairly easy mission: he had to find out the cause of the numerous deaths of various creatures and cyborgs near one of the farms where genetic research was conducted on various plants. Most of the corpses had the back of their necks chewed out, along with the medulla oblongata. By the way, several cyborgs died due to similar injuries. Arriving at the site, Jack found huge abandoned hangars and greenhouses that covered several acres of territory. The owner moved out a week ago to find someone who would solve his problem with an unknown predator.
Jack spent two days exploring the area until he came to one of the greenhouses, which was covered with vines. He caught only a few rustles and a movement on the periphery as something closed around his neck, and the back of it was pierced by so much pain that the mercenary lost consciousness. He comes to his senses only a few days later. It was dark all around. He wasn't wearing any pieces of clothing or equipment. They were all lying around. Red spots swam before his eyes. Jack tried to get up, but immediately fell to the ground. Feeling the back of his head, he found something that looked like a metal brace. And that something stirred. Jack experienced a real horror and panic, jumping to his feet and trying to rip it off, however, the back of his head itched and his body began to change. It hurt like hell as the skull and bones began to change shape, and the world around them exploded with hundreds of completely different colors. Thick chitinous plates covered Jack's entire body, covering his vulnerable spots and almost completely replacing his fur. Only a few areas remained covered with roughened skin to ensure the flexibility of the limbs. The claws strengthened, and the tail lengthened, becoming forked and also covered with chitin. The mane on Jack's back and limbs was a dirty gray color, making him almost invisible in the dark and twilight. Prehensile and very strong limbs and tail made it possible to move on vertical surfaces, clinging to the smallest ledges. The view, thanks to the numerous eyes on one of the plates of the skull, expanded significantly. Jack was now able to distinguish between infrared and ultraviolet light. His saliva dripping from his long tongue burned the grass beneath his feet like acid. The speed and strength increased by about three times after this transformation. The mercenary was able to reincarnate back only after he completely calmed down and came to his senses. He immediately returned back.
Kel examined Jack and found out that a parasite was attached to the back of his head, which connected with his nervous system and in case of danger, he transforms Jack's body to ensure his invulnerability and his own. By a happy coincidence, it was the artificial body that turned out to be compatible with this parasite, unlike its previous victims. However, at the moment, no one knows how to separate it from Jack's body. This creature combined their circulatory and nervous systems, using the mercenary as a breeding ground and protecting him with all its might.