From the Super Mario Wiki
Dogu is the final secret opponent in the game Wrecking Crew '98. As his name implies, he is a Dogū. His stage, "stage D," is reached by defeating the other secret opponents, Onigiri, Onnanoko, and Oyazi in stages A, B, and C. Upon arrival, Dogu levitates in and tells Mario that he is an ancient being from a faraway land, and issues a match over having been awakened from his slumber. Once defeated, Dogu seemingly malfunctions and explodes in multiple pieces, although rematching him shows that he was able to repair himself. Dogu is also unlocked as a playable character in VS. Mode and Tournament Mode.