Elder Princess Shroob

The Shroobs are actually led by Princess Shroob's twin sister, who got sealed in the Cobalt Star and broken apart by Princess Peach herself. After Baby Bowser put all the pieces of the star back together, the older Princess Shroob regained her power, fighting the brothers on a flying platform high in the sky. She is much stronger than her sister, and commands a fleet of Shroob saucers. Her attacks depend on how many saucers are present; she can use one to heal herself with a drink, or summon a Chain Shromp to attack Mario, Luigi, Baby Mario, and Baby Luigi. She can ride on two saucers, shooting energy blasts down on the brothers, then firing blasts at the brothers from the sides, before being blown from the UFOs and landing on the platform, causing a shockwave. She can also have three UFOs bring her a Shroob meteor, with which she attempts to crush the brothers; however, this attack is easily defended against, and leaves her open to damage. Even without saucers, Princess Shroob can charge either brother. Princess Peach throws stars to the brothers, with which they can knock saucers out of the sky and prevent her from using her more powerful attacks.

Once she loses 3500 HP, the player will have to have to eliminate her stronger form with 3000 more HP. In that form, she has seven parts: four arm tentacles, a group of leg tentacles, a crown, and her main body. In order to make her vulnerable, the player must eliminate the leg tentacles, and then the crown, which is the source of her power, before they can attack the body. Princess Shroob's attacks vary depending on which body parts are involved. Her arms can grab or stab the brothers. Her leg tentacles can spin on the ground (two to four at a time). Her head can shoot poison gas, shoot down saucers which hit the brothers, or create an energy orb and drop it on a brother; the latter two attacks can be countered.

When the player defeats her and, Baby Luigi claims her mushroom remains, returning to the present, an unconscious Bowser eats the remains and turns into Shrowser, a combination of Bowser and the spirit of the Elder Princess Shroob. This fight is unique because, as Bowser says, you cannot attack. In order to defeat Shrowser, the player must Jump over or hit back 20 fireballs, 10 fire orbs, or some combination of the two (e.g. 12 fireballs and four fire orbs), which destroy the spirit of Princess Shroob, causing Bowser to lose his power.