Because of his little screentime, Luigi's full personality is mostly unknown, but from what we've seen from him, he appears to be a sadistic, arrogant and manipulative traitor, as he's constantly been fooling and tricking Mario into believing he's on his side. In his final moments, he shows arrogance after proudly posing over Mario's body before being thrown into the lava and screaming his last, haunting words. He’s also rather petty, as his main motive for wanting Boyfriend and Girlfriend dead