The Mascot Costume is a costume that Sly gets in Sly Cooper: Age of Thieves in the episode Alice in Cooperland.
The Mascot Costume is essentially the kind of costume one would see in theme parks, the kind that allows people get autographs from children. It is essentially a big dodo costume with a large head and the Sly Cooper logo on the back of its head. It comes with an autograph book on its left hip.
"When Ven St. Claire was building Wonderland, he made sure everything was perfect, including the costumes. This costume in particular is especially good, with enough charm to get even the guards to want an autograph. Rumor has it that the autograph book is bewitched; any guard that jots his or her name in the book essentially becomes a mind-controlled puppet and can be used to disable certain traps or devices."
Pressing the circle button lets Sly take out the autograph book, but before the book can be used, Sly must press the square button to dance. This will attract certain guards, depending on the amount of dancing. When a guard has been brainwashed, press the L1 button to have the guard run forward, destroying certain booby traps in Sly's way. Pressing the R1 button makes the guard attack other guards in the area.