Elder Princess Shroob is a fictional character in the Mario series and the final boss of Mario & Luigi: Partners in Time. She is the leader of all Shroobs and twin sister of Princess Shroob. When Princess Peach, Toadiko and Toadbert came to the past Princess Peach's Castle they met the Shroobs. Elder Princess Shroob attempted to attack Peach; however, Peach used to power of the Time Machine, the Cobalt Star to trap the Elder Princess Shroob inside. Peach then shattered the Star into pieces; however, the younger Princess Shroob still was able to capture Peach and trap her in Shroob Castle.
Throughout the game, Mario, Luigi, Baby Mario and Baby Luigi collect the various pieces of the Cobalt Star, not knowing that Elder Princess Shroob is actually trapped inside. When the brothers get to the top of Star Hill, the spirit of the Cobalt Star appears and speaks to the brothers. The spirit is actually revealed to be Elder Princess Shroob who was tricking the brothers. It seemed that only Baby Luigi knew since he was crying when "the spirit of the Colbalt Star" appeared.
Finally, at the end of the game, after Princess Shroob is defeated, it is revealed that Princess Peach kept the center shard of the Cobalt Star. Peach states, however, that she cannot allow the Cobalt Star to regain its original form. Before she can explain, Baby Bowser comes in and steals the last shard, combining it with the five that the heroes had already collected, causing Elder Princess Shroob to come back to life. The baby and adult brothers then fight Elder Princess Shroob on a platform high in the air.
She is much stronger than her sister, and commands a fleet of Shroob UFOs. Her attacks depend on how many saucers are present; she can use one to heal herself with a drink that recovers 120 of her HP, or summon a Shroob-like Chomp to attack Mario or 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 at either brother. Sometimes she stops just before she's about to tackle the brother which could cause the player to use the hammer to soon. 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, she activates her crown and morphs into a hideous beast, which is her true form. 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, which allows the crown to be attacked. This crown is the source of her power, as trying to attack the body before taking out the crown results in minimal damage. Once the crown is deactivated, Princess Shroob herself can be attacked. In this state, 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 finally defeats her, Baby Luigi claims her purple Mushroom remains. The party return to the present Peach's Castle where they find Bowser's unconscious body. The purple Mushroom from Baby Luigi's pocket suddenly floats up and goes right into Bowser's mouth. Bowser and the Elder Princess Shroob then form into Shrowser and the brothers battle Shrowser. Shrowser is easily defeated. The game then ends with the babies (including Baby Peach) and Young Toadsworth finally returning to the past.
Elder Princess Shroob seems to have cared a lot for her sister (who, ironically, made no effort to put back together the Cobalt Star) and swears her life into avenging Princess Shroob's death. Oddly, she shows no care at all for her own people. Whenever a Shroob UFO performs a task for her, she will smash it, killing the pilot, even for simple tasks like bringing her a drink. When she turns into a beast, she is even more destructive, shooting down her own UFOs so that they will hit the Mario Bros.
- When the Elder Princess Shroob is in the "spirit of the Cobalt Star" form, she resembles Misstar, the Star Spirit from Paper Mario and Mario Party 5.
- One of her attacks involves her spitting out a beam at the UFOs above her head. Some will be electrified, and some burning. The burning ones would fall on Mario, while the electrified ones on Luigi. This is possibly a reference to Mario's Firebrand ability and Luigi's Thunderhand in Mario & Luigi: Superstar Saga.
- The second form of Elder Princess Shroob has some attacks that are similar to the attacks of Cackletta's second form. These include such things as firing a large orb at the Mario Bros. and swinging arms/tentacles. They are also similar in that certain bodyparts may be destroyed to make their battles easier.
- In the North American version of Mario & Luigi: Partners in Time, the Elder Princess Shroob's crown is given an attack rating, although the crown never actually attacks. In the Japanese and European versions of the game, this has been corrected, as the crown has a Power rating of 0.