Roxx is the assistant of the Illuminati. As seen in episode 15, he's given a task because there's less chaos going on. So he is supposed to bring more chaos back.
Roxx seemed to act very off when meeting Brianna. He seemed very kind to her as a matter of a fact. When Squidward arrived with some news about money, Roxx got real jealous and angry. He later made up his mind, and he was about to destroy the city before the crowd showed up. He beat up Mario very badly, and dodged every punch Mario threw. He was defeated by Illumiweegee.
His new target ended up being AGK, after news from the Illuminati. He got distracted about Scan when he noticed him right next to AGK. He told AGK instead that if he doesn't bring Mario, he will kill AGK. AGK ignored and ran away. He never got to do his task, because Angry Sun blasted him away.
For thousands of years, he has been working with Illuminati way before the team even grew. And his first ever victim was a guy named Branch. The oddest thing is Branch originally looked like Roxx. He was the mastermind behind Branch's whole 10000 year wait. He set up the poisonous gas, and put Branch into the ground.