Here is the boss appearance idea:
Since Onaga (dragon race) and Li Mei (human race) got married at the end. I would like to see a somehow unisex boss known as "larva monster" where his/her lower body is a long larva (snake body shape) and the upper body has two heads that have snake tongs with a human muscular male chest and two arms. First head is a female and looks a bit like Li Mei (in her second costume from MKD). Second head is a male and looks a bit like Onaga. This boss is an average body size one, a bit bigger than a human size and not as huge as Onagas body size.
Here is the boss story:
Unfortunately, Li Meis boby transformed into an (evil) bigger size during her pregnancy cycle because of Onagas strange/monster hormones. While Li Mei gave birth to her child, he/she came out as an egg because of the Dragon Kings Dinosaur origins. Meanwhile, the egg was hidden in a secret volcano place. But after several months, Onagas enemies which are on the good side, discovered the secret place and decided to kill the child before he/she will be mature/strong and goes out from the egg. However, Onagas enemies could not get so far in killing the infant, they reached only by cracking the egg because by coincidence the Dragon King and Li Mei were heading towards the egg at the same time their enemies were heading to kill the weak or immature monster. In the meantime, Nitara was supposed to be the guardian of the egg, she was nearby the egg place and heard someone coming toward the egg. So, Onaga and Li Mei joined later by Nitara went into a fight against their enemies at the egg place while the larva was already outside the egg after its shell was totally broken. Now, Li Mei and Nitara won the fight whereas Onaga died during the battle and the larva monster should have died too but he/she didnt because one of Onagas sorcerers managed to put a spell on the larva monster and make him/her stay alive. The spell has rules that the larva monster will be alive but will not grow up or change anymore, he/she will remain the same and will not transform into a two headed dragon fly.