Chimera
Out of every monster that Isaac had seen since the game started, there was one that still left a deep impression on his head. A monster that was quite troublesome for him and Gavin. No matter how much weapons or magic hurt it, the monster would not die.
The scratches healed. Its missing body parts would grow in seconds. The monster continued to regenerate its body until it recovered completely.
The monster was a Chimera.
There was only one Dungeon Master who had it. It was Earl Xenovia.
Isaac remembered, in the third year, there was a dungeon break in Tianjin. Earl Xenovia unleashed various experimental monsters; they all had strange shapes and abilities. Of course, the hunters had difficulty fighting them.