Nerdy is the main antagonist in A day with Bowser Jr. He is a rival of the Koopa family (especially Bowser Jr) and he is the leader of the Mario Fan Club, and uses its members as minions or assistants.
He is voiced by Daniel.
Nerdy is unpleasant, scheming, vengeful, smart and sadistic. At the beginning of the series he was potrayed as merely a stereotypical nerd: unpleasant and selfish. But as the series progressed, Nerdy became more cruel and vengeful as a result of Bowser Jr always ruining his moments. Nerdy is also smart and cunning, and his plans are very unpredictable for Bowser Jr, who is fairly less smart than him. Aside from these negative characteristics, there's a nicer side of himself shown mostly with his friends at the Mario Fan Club.
Nerdy's biggest trait is his intelligence, which allows him to come up with plans that are impossible for Bowser Jr to anticipate. However, Nerdy lacks in physical strength and is not able to win in a bear handed fight with Bowser Jr (but he can resist for a long time).
As the Mario Fan Club leader, he is a very passionate fan of Mario (interestingly, not the franchise, but the character himself).
- In First episode (Part 1) and First episode (Part 3), Nerdy's face disintergrates.
- In First episode (Part 1), Nerdy's face turns into a skull after Nerdy's face touches the garlic power reflected by Bowser Jr's shell.
- In First episode (Part 2), Nerdy's face was still a skull.
- In First episode (Part 3), Nerdy's skull turns into a brain connected to a red tube after Nerdy's skull touches the garlic power reflected by Bowser Jr's shell.
- In Living with Nerdy (Part 1), after lots and lots of plastic surgery, his face was finally back, so he 'won'.
- In Living with Nerdy (Part 1), after his house was destroyed, he started living in Bowser's airship.