Ideas for the WerepireJack auAnti causes Jack to become a Werepire. Earlier in the day Anti gets bored and snoops around in Jack's mind. He ends up finding a mysterious old wood box wrapped in chains with celtic words carved into the wood. Being curious, he opens it. Two black spirits resembling a wolf and a bat fly out of the box and run off, dissapearing. These are the same spirits Jack sees in his nightmare. They represent the werewolf and vampire genes in his dna. The chest had been his humanity, keeping the spirits, and thus his werepire genes, locked up and dormant. By opening the chest Anti allowed for Jack's werepire genes to wake up, causing Jack to change later that night. Please note that in the Old Blood story this is not what happened. This is an alternate explanation as to why Jack changed.
Werepire's are sometimes able to transform into a wolf with bat wings, though in wolf form the wings aren't large enough to be used for flight. I am undecided as to whether or not Jack will have this ability or no
Old Blood: a Jacksepticeye oneshot Jack tossed and turned frantically in sleep, breaking out into a cold sweat as his blankets got tangled around his legs. ~Run, all he could do was run. He could hear them, those things were practically right on his heels. His was breath coming in gasps as he ran, darting around obstacles as he tried to escape what was chasing him. He saw an alley up ahead and darted into it, hoping to lose his pursuers. He skidded to a halt when he saw it was a dead a dead end, quickly turning around when he heard them enter the alley behind him. He back up in fear, back meeting up with the brick wall as they approached. Two beings seemingly made of shadows. One a large wolf with molten gold eyes and long fangs. The other a freaky looking bat with glowing green eyes, the pupils slits. Jack let out a scream as they lunged for him, sinking their teeth in either side of his neck.~