Hamill danced again Tuesday, and Yamaguchi joined her.
"It's such an honor to join my idol out here on the dance floor," said Yamaguchi, the Season 6 "Dancing" champ.
Korean pop star Psy brought his unique moves to the ballroom by dancing along with his new single, "Gentleman." Pitbull and Jessica Sanchez also performed.
ABC announced earlier this month that the next season of "Dancing With the Stars" will air one night a week instead of two.