Vattroller X is a japanese exclusive Action RPG game released for the GBA in 2004. It is based in a V-Jump manga that seems to be very obscure in the west.
The battles in this game are played in a top down perspective and the player has to hit the opponents with combos and charged attacks until they run out of HP. When that happens, the knocked out character turns into a ball. Whoever manages to send the ball into one of the arena's pits scores a point.
The game features a RPG mode in which the player picks a character to customize. To unlock it, the first three chapters of story mode must be finished. There's some content in the game the can only be unlocked by passwords... found in the series' japanese card game.
Official site (JP)