Mellohorn

Mellohorn is the evolution of Mellon. As such, you need to obtain Mellon from the blue Petball and use 300 Candies to evolve it into Mellohorn.

Biology
Mellohorn seems a lot like Mellon, except it turns pink, it's eyes turn purple, and it gains horns.

Moveset
The battle system isn't out yet, but based on it's description, it will know an attack called "Belly Swing."