Magic Paintbrush

"This...is my magic brush. When I draw with this, all my wishes come true! A strange old man in a white coat gave it to me..."

- Bowser Jr.

The Magic Paintbrush, also known as the Gaddbrush, is a weapon wielded by Bowser Jr. in Super Mario Sunshine. It was created by Professor E. Gadd and is emblazoned with his logo; its ferrule also bears a passing resemblance to the head of another one of his creations, F.L.U.D.D.. Unlike other E. Gadd devices, the paintbrush is wielded as a destructive implement, and produces toxic Graffiti that was used by Bowser Jr. to defile Isle Delfino in Super Mario Sunshine.

Super Mario Sunshine
After obtaining the brush from E. Gadd, Junior used it to paint Graffiti of various shapes (including " △ "s, "O"s, "X"s, and "M"s) all over Isle Delfino under the guise of Shadow Mario. He then placed the blame on Mario, who was sentenced to cleaning up the entire island as community service before being allowed to leave. Mario used F.L.U.D.D. to accomplish this, before defeating Junior and his father in a final battle atop Corona Mountain.

After the final battle, Bowser Jr. dropped his paintbrush, which was later discovered by Il Piantissimo near Gelato Beach.

Sports
Bowser Jr. somehow recovered the weapon prior to the events of Mario Power Tennis, where he used the brush to perform special moves. Bowser Jr. used it again in Mario Hoops 3-on-3 in his Special Shot, called the Graffiti Shot. The Magic Paintbrush also appears for Jr's Special Shots in Mario Sports Mix.

Mario Super Sluggers
The Paintbrush once again appears as a prop in Junior's Special Shots in Mario Super Sluggers, and can also be used as a bat, replacing his little spiky bat from the predecessor. There is also a minigame called "Graffiti Runner" where the player finds the Brush and uses it to paint the floor the player's color to win. If the player uses all the paint, the player loses it, so the player has to grab it again to continue.

The design of the paintbrush is slightly different in Mario Super Sluggers, as it lacks the decorative crimp (the spiked cylinder emblazoned with E. Gadd's logo), with the silver funnel containing the bristles connecting directly to the handle.

Mario & Luigi: Dream Team
The Magic Paintbrush appears in Mario & Luigi: Dream Team, in the form of one of Bowser Jr's attacks, where he tickles Mario or Luigi to steal one of their Bros Attacks.

Mario Kart Arcade GP
Several Magic Paintbrushes appeared on display in Mario Kart Arcade GP's Diamond City course.

Mario Golf: World Tour
In Mario Golf: World Tour, Bowser Jr. uses the weapon in all his post-hole animations except Par.

Super Smash Bros. for Nintendo 3DS / Wii U
In Super Smash Bros. for Nintendo 3DS / Wii U, Bowser Jr. and the Koopalings use the paintbrush in their Final Smash, where they transform into Shadow Mario and paint a giant graffiti X on the screen, which hurts anyone who touches it.

Trivia

 * When Bowser Jr. masquerades as Shadow Mario, the Magic Paintbrush changes color to match his shadowy consistency. It is only when he becomes Bowser Jr. again that the true coloration of the Magic Paintbrush is revealed.
 * The Magic Brush can be seen as Bowser Jr's equivalent to the Koopalings' Magic Scepters in Super Mario Bros. 3, as they are all magical devices obtained from protagonists by Bowser's children in their debut game.