Nana can be killed if she does not land on a stage, especially if the Up + B move is used. If Nana and Popo become seperated you can easily kill Nana by attacking her and keeping her seperated from Popo. It should be noted that the Ice Climbers' Percentage bar will not go up as that is Popo's. Nana has a hidded bar. Another thing is that if Popo is killed, when the game knows Popo died, even if Nana is still alive, Nana will vanish in a puff of smoke and will reappear with Popo on the recovery board