The Winkle Colosseum is a place in the Chucklehuck Woods where many Winkles compete. During the course of Mario & Luigi: Superstar Saga, one of the four pieces of the broken Beanstar lands inside the Colosseum.
Mario and Luigi came to the Winkle Colosseum to look for the piece, and were forced to play a mini-game for a fee of 500 Coins. After they completed the game, the Winkle guarding the door gave the brothers a Winkle Card, allowing them to pass to the Winkle Area, where the Beanstar piece was.
There they found Popple, who had already seized the Beanstar piece. Mario and Luigi battled him for it, and even though Rookie wasn't around to assist Popple, the fight was still challenging. However, Popple was eventually defeated and forced to flee, leaving the Beanstar piece for the brothers.