Medley Princess is Trill's Daydream, whose main trait is to be a powerful transformation for her. This jester form is one that can only reach its full power during the night thanks to the power of the stars, and through that she acquires the ability to summon musical instruments that she can use both for music and for combat. Medley Princess' instruments are bound to her and disappear once Trill goes back to her regular form.
Besides that, Trill also gets a noticeably more powerful physically while transformed into Medley Princess, becoming stronger, more agile and more resilient.