His mother, Chicha, is pregnant with him for almost the entire movie, but by the end, she's already had him.
In the episode "Clash of the Families", Yupi is revealed to possess inexplicable superhuman strength. This is first evidenced while Kuzco is exhorting Pacha and his family to train harder to win the 'Famaolympics' inter-family competition, stating that "our secret weapon over here can't do it all"-- at which point Yupi is shown tossing his mother Chicha head over heels in midair and catching her over and over again, ignoring her flustered pleas for him to put her down. Later, Yupi demonstrates his incredible strength once again during the final event of the competition. When Kuzco hints that he still can't help but want to win the event, Pacha mentions that it might be nice to win for a change, at which point Chicha merely says, "Yupi? Make Mommy proud." At this point, Yupi takes his oar and begins paddling at super speed, effectively becoming a living motorboat engine. His paddling alone proves enough to cause the Team Pacha canoe to partially rise up out of the water, prow-first, and go rocketing ahead of all the other competitors.