Bakugan Battle Brawlers (2007) : 2x29

While Dan is shocked by a surprise visit from his father and Mira reminisces over Keith, Ace searches the city for a place Baron can stay. As he approaches a future building site for an apartments complex, Baron calls Ace and tells him how the Haos Energy was stolen by Hydron. Then Mylene appears and challenges Ace for the Darkus Energy. As the battle drags on Ace and Midnight Percival eventually become overwhelmed by her mechanical bakugan. Before Mylene can execute the final blow, Sirenoid appears from the lake below them, moments before Klaus, and joins Midnight Percival in battle. With their combined efforts, they manage to drive Mylene away, right after she says she will return with the rest of the Vexos for the Darkus Energy. It is revealed Klaus helped Dr. Michael develop his dimensional transporter system. After meeting up with Sirenoid, his foundation continues to fund the scientist's research as well as managing timeshare on Vestal. By the end of the episode, Baron had arrived to join them and Ace has become frustrated with Klaus's constantly calling him 'boy'.