In the episode, when the Koopa Packs have Mario and Luigi surrounded, Princess Toadstool gets a Starman and becomes Super Princess. The color of her dress changes to red, blue and white, and Super Princess becomes more powerful. She was able to defeat the Koopas single-handedly.
The Princess says "Princess P. to the rescue!", after getting the star, which is a nod to the name "Peach", which had only been the princess's name in Japan at the time prior to Yoshi's Safari introducing the name to Western territories (albeit unsuccessfully, until Super Mario 64 later reintroduced it and successfully popularized the name and helped make it the current universal standard, slowly phasing out the Toadstool moniker in the process).