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“Undodog will help you correct a minor mistake by cancelling your last action. You will quickly find that this hound is a great friend.”
Undo Dog (referred as Undodog in earlier appearances and Undo in the PAL region versions of Super Mario Maker) 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, Undo Dog will sometimes sneeze loudly. According to the instruction manual for the game, this is because of his allergies. 
He reappears in Super Mario Maker, 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 Undo Dog 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.
Names in other languages