Boudacians are the alien warrior-race that Princess Mandie hails from.
Very little is known about Princess Mandie's actual race. However, they are shown to have destructive tendencies as evidenced by Princess Mandie herself, and a visual sequence showing their intent to destroy Earth alongside the Yugopotamians. They like marrying into the royalty of other alien races in order to strengthen their empire and become more powerful.
Female Boudacians are greenish-yellow skinned, have lavender colored hair, and two bug-like antennas on their foreheads and triangular teeth. They are considered very beautiful by human and fairy standards, but hideous by the backward Yugopotamian standard. Mandie's father has red eyes and brown hair all over his body. As he was the only male seen, it is unknown if they all look this way.
Boudacia is the homeworld of Princess Mandie and the Boudacians, a race of warrior-aliens. Not much is known about this planet, as it has only been referenced and not seen, but it can be assumed that the planet is nearby Yugopotamia since the inhabitants are in close contact with each other.
The people of Boudacia are likely a warrior people, since they are ruled by a fierce warrior Princess. The name "Boudacia", which is a pun on "Bodacious", likely suggesting the inhabitants are very good looking, and therefore disgusting by Yugopotamian standards.