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

Young drakes 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 marks the beginning of maturation. At this point they are often capable of hunting on their own.

When Voldemort the Undead became a zombie he was sure he would be able to revive at will and continue to wreak havoc as he always had. Unfortunately Failed HorcruxoftheDead, who had tried to follow him into the void, managed instead to hold on to one of Voldemort's horcruxes, and so although Failed failed to follow him, he did at least ensure that Voldemort cannot return. This annoys Voldy very much, but there's nothing he can do about it, except be exceptionally nasty to any new undeads who show up.