Where is the last person for limited robo battles in Custom Robo Arena

You will have to battle: Polly, Serene, Marv, Cheepers, Duncan, Billy, Shipley, Winchell, Stark, Kris, Tamara, Angelica, Halburn, Lunax, Terrax, Solax, Mr. Stubbs, Dennis, Tanya, Dickie, Eddy, and Liv. Eventually you can go underground and purchase illegal parts, and there are some people to face there but I'm not sure if it's necesary to defeat them, I haven't gotten that far:)