It’s an undead baby dragon, produced by a failed magical spell. It probably would be cute if it weren’t partially decayed.

Young dragons are relatively defenseless. They are born with relatively soft scales, which are shed and replaced with harder ones as the hatchling matures. Once a hatchling’s wings grow in, it typically marks the beginning of maturation. At this point they are often capable of hunting on their own and are usually left alone by their mother.

It was a dark and stormy night when an egg was brought to the clan's cave by the vampires. After the small dragons had hatched they were left to die; sacrificed. All for the sake of Caius wishing to temper with life and death, all to see the limitations of their magic. Bringing back a loved one from the death is what most may wish for after all. That is what they too wished for.

During All Hallows Eve, the magic used on the dead body worked. Perhaps not fully; still, the results were exactly what Caius wished for.

The young lad, who had been left to die, was brought back from the afterlife; his once living body was turned into a walking corpse. This lad is in fact not a lad; he merely sees himself as such while in reality no one can know for sure what he is. TLJ, as he later was named, usually only referring to himself as "L", is a silent lad who won't make much noise. He prefers to observe things from the shadows. One could say he's a thinker, planning things that have not yet occurred.