Compared to other Shroobs, Princess Shroob has a tall, human-like build, though keeping their general face features and two-fingered hands. Her mushroom cap has another, smaller one on top, looking like a bun hairstyle; the spot in the middle has the shape of a crown and a round black jewel on it. She also has large white lips and often carries a metal chalice with two horn-like protuberances at the base and round red gems around it. She wears a magenta dress similar to Peach's, with slightly darker panniers and a large high collar; the hem and the sleeves have a lighter swirl pattern, while on her chest is an oval shaped brooch with a black gem and a silver ring around it. She also wears small, round green earrings and long white gloves. She is also frequently seen holding a blue and yellow microphone with a visibly broken cable.

As the primary antagonist of Mario & Luigi: Partners in Time, Princess Shroob is a militant conqueror and is shown to be highly aggressive (e.g. shooting down the Koopa Cruiser), though most of her dialogue is undecipherable. In addition, the Shroob race acts as her loyal subordinates, serving her drinks and always following her commands. She is willing to go to any length to conquer the Mushroom Kingdom, such as attacking Toad Town and draining its citizens of their vim. She also takes revenge on Peach for capturing her twin sister and imprisoning her in the Cobalt Star by capturing her, then planning on feeding Peach to Petey Piranha in front of a Shroob audience.

It is unclear whether or not Princess Shroob cares for her older sister; she did not attempt to rebuild the Cobalt Star the [Elder Princess Shroob] was trapped in, and referred to the Mushroom Kingdom as belonging to her rather than her sister.

As the commander of the Shroobs and one of the final bosses of Mario & Luigi: Partners in Time, Princess Shroob is powerful and she often uses the Shroob army to her needs. By herself, she demonstrates various energy abilities, such as throwing energy balls, flying, and controlling stars in her boss battle. Princess Shroob also shows technological skills via the use of her throne. In addition, she can disguise herself as Princess Peach to fool the characters, despite the disguise having a Shroob mushroom on her face.