Rainbow Brite is the main antagonist of the "Game Over" Robot Chicken sketch, one of the longer sketches in the show and one that had Rainbow Brite depicted as a much more malicious character than she was in the original show - this is common for the show, which gains its humor from gross-out and/or offensive parodies of popular media.
"Game Over" begins with Murky Dismal and Lurky in a bar, depressed over not being able to do evil - the barman tries to convince them to give up their quest to "make the world grey" and suggests arson as a "real evil" deed: which horrifies Murky and the pair leave.
Murky decides to raid Rainbow Brite's home alongside Lurky but the two can't find anything worth stealing, the pair then panic when Rainbow Brite arrives home unexpectedly and they hide behind a sofa.
Rainbow Brite proceeds to reveal her true self, a drunken, ill-mannered, and abusive woman - when Murky and Lurky try to escape they attract Rainbow Brite's attention and she proceeds to brutally murder them both with a chainsaw.
The next day Rainbow Brite addresses the crowds, claiming Murk and Lurky had changed their ways and went to Tibet to help fight oppression - which works and thus she effectively gets away with multiple murders.