Undodog

Undodog (also referred to as Undo Dog) is a helpful character in Mario Paint, selectable as an icon in the bottom toolbox in the Art and Music modes. His appearance is that of a tan dog with a thin black box around his neck, like a collar, probably representing the outline of his icon. His name is a pun on the word "underdog", and a portmanteau of the words "undo" and "dog", and, as his name states, he helps the player undo the last action. He will also dance and jump around at the bottom of the screen when the player is idle in the stamp editor or drawing board color selection. He will quickly run back to his original location if the player moves the mouse. If the player turns the game's music off and leaves it silent, Undodog will sometimes sneeze loudly. According to the instruction manual for the game, this is because of his allergies.

He reappears in Super Mario Maker and Super Mario Maker for Nintendo 3DS with the same function as his original appearance: reverting the player's last edit. In this appearance, he wears a white box resembling an Elizabethan collar instead of a black box. He also appears throughout the game outside of the course editor such as in the game's manual with Mary O and Yamamura, riding a rocket in the background in Course World and when a player completes the 10-Mario or 100-Mario Challenges, and in the corner during Gnat Attack. When 10 seconds remain on the timer in Gnat Attack, he'll start barking and jumping excitedly. If the player shakes the heart SFX, its icon will turn into Undodog wearing a surgical face mask. This SFX will cause static to appear briefly with a buzzing sound followed by the course's music turned off temporarily (or permanently, if it is equipped to Mario). The icon and the music being turned off is a throwback to Mario Paint where the bottom lever in the background music option has a similar appearance and effect when selected. A special event course titled "Walkin' with Undodog" also exists.

Undodog reappears in Super Mario Maker 2, which also sees him in a larger role in the game's story mode (appearing for the first time as a 3D model), providing Mario access to various jobs to help rebuild Peach's Castle. Undodog can also be seen in the background of nighttime levels in the snow theme riding a rocket.

Undodog makes cameo appearances in the WarioWare: Touched! microgame, Mario Paint, and his icon can also be seen in the WarioWare: D.I.Y. microgame for Mario Paint.

Trivia

 * The Mario Artist series also uses a dog's head as the "undo" icon; however, the dog bears more resemblance to a beagle than it does to Undodog and may not be the same character.
 * While Undodog himself does not appear in Super Smash Bros. for Wii U, his sneezing sound effect is incorporated into the "Mario Paint Medley" music track.