Brionne is a light blue, pinniped Pokémon with three ruffle-like growths around its body. The first ruffle is just under its front flippers, while the last is shortly before the tail. The ruffles alternate white and pale blue. Its long ears are made up of three segments that lighten and increase in size towards the tip; the first segment is ovoid, while the latter two are spherical. It has a long, conical snout with a white tip, a spherical pink nose, and large dark eyes with pinkish pupils. Its front flippers are much longer than its tail flippers, although both have white tips. There are three digits on the front flippers.
While Brionne normally learns to dance from members of colony, it can also learn to dance from humans. It works hard to memorize each dance through imitation. It is capable of dancing in perfect time with others, even if it's never danced with them before. Large groups of Brionne can be seen dancing together on moonlit nights. Its battle strategy consists of dancing while creating water balloons. The dance confuses the opponent, and during this weakness, Brionne slaps the balloons toward the target where they explode. Only those who have earned its trust can see this Pokémon when it is sad. It will otherwise always act cheerful and never allow its sorrow to show.