I bet that many of you didn't expect this, but it was a bit obvious, remember that Hunter is wopter's brother, he's able to transform as well, the reason why he didn't do it before was because he didn't need to do it, he was much more powerful than wopter, but since wopter reached his semi level 3 he matched hunter's strengh, maybe surpassed it a bit, after that, Hunter realised that he had to train to get more powers but he was at his limit in his normal form, that's why he needed to learn a new transformation to be able to hold more power.
Wopter would never stand a chance against him in his second level