Mona Lethal is a battle/fighting robot whom was a very popular robot for her design and strength. Robotboy fell in love with her after finding her attractive, and when he heard that she was going to be on the Robo-Con, he went there to see her. Then when he signed for the robot battles and won every single match, he had to face towards her to fight with.
At first, he didn't fight to her because he liked her so much, until he finally attacked her when she almost killed Tommy and Gus for stopping her from destroying Robotboy, and thus, he defeated Mona while being super-activated.
She appears to have a pretty skinny body shaped like a bow, with big eyes and blue lips.
- Apart from her cameo in "A Tale Of Two Evil Geniuses", she also makes a cameo on the episode "Bad Language" on a CD-folder that Robotboy received from Kamikazi.
- She has physically appeared in two episodes along her non-physical cameo on "Bad Language".
- Her name is a pun on the famous Italian painting, Mona Lisa, by Leonardo da Vinci.
- She's one of the villains that Lola has never met or been mentioned to.