At the end of a tournament when Dan makes the player an official Bakugan Battle Brawler, Marduk is revealed to have allied with Hal G, Masquerade and Naga in order to defeat the Battle Brawlers and rule over the worlds and the Bakugan. Right after Naga got the Silent Core, the seals that held Vladitor captive in the Doom Dimension suddenly broke and he escaped from the Doom Dimension. In several fights the player will meet a lot of people but at the same time a Darkus user, whose name is Marduk, Desires to rule over all Bakugan together with Vladitor, another Bakugan that suddenly appears. Leonidas is an unknown and aggressive Bakugan that was created by all the hate and anger of the lost Bakugan trapped in the Doom Dimension. (Leonidas' attribute depends on what attribute you chose). After going to the local store and meeting Alice, who suggests the player should battle with other brawlers in the park to earn BP (Bakugan Points, the game's currency) a strange Bakugan called Leonidas gets teleported to the park, who is now the new best friend of the player. In all other versions, you get a Serpenoid, a Juggernoid, and a Saurus that match the attribute: Pyrus, Darkus, Haos, Aquos, Ventus, or Subterra you chose at the start of the game). (In the DS version, you get a Pyrus Serpenoid to start off with. One day the player's character meets Dan Kuso, one of the Battle Brawlers, who teaches him the rules in a fight against Shuji.
