Elder Princess Shroob
“FOOLISH MUSHROOM HEADS... YOU MAY HAVE BESTED ME, BUT THE SHROOBS WILL LIVE ON... ONE DAY, THE SHROOBS WILL DANCE ON THE BURIED REMAINS OF THIS PATHETIC KINGDOM...”
Elder Princess Shroob and her younger sister are the leaders of the Shroobs, an alien race that invaded the Mushroom Kingdom. When Princess Peach, Toadiko and Toadbert came to Princess Peach's Castle of the past, they met the Shroobs. Elder Princess Shroob attempted to attack Peach; however, Peach used the 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.
 Mario & Luigi: Partners in Time
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 Cobalt 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 gradually come back to life. During her transformation, Peach tells Mario and Luigi the long-awaited truth. 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; with just one, she can heal herself with a drink that recovers 120 of her HP (in the Japanese and European editions, she drinks 80 HP), or summon a Shroobified enemy called a Shroob Chomp to attack Mario or Luigi. The UFO guides the chomp towards a brother and the player has to quickly see which way the UFO is going. With two saucers, she can float up in the air, shooting energy blasts down on the brothers, which are too fast for both brothers to jump at the same time so the brothers need to check which hand the large evil princess shot it. She'll also fire blasts at the brothers from the sides, which needs both bros to jump if the princess isn't lined up with the top of her throne (which she commonly to trick Mario and Luigi) before being blown from the UFOs and landing on the platform, causing a shock-wave needing the brothers to jump at the same time. With three UFOs bring her a Shroob meteor, with which she attempts to crush the brothers; however, this attack is easily defended against, with the Hammer and leaves her open to damage. Princess Peach throws stars to the brothers, with which they can knock saucers out of the sky and prevent her from using many of her attacks.
When there are no saucers, the princess does one of her most dangerous moves: A football tackle towards one of the plumbers. The younger versions of the plumbers then have to hammer her away multiple times (usually two) before she finally resents. Also only the last strike counterattacks. Occasionally she will do a tricky if-not-extremely frustrating tactic of stopping right before the targeted brother, tricking him into swinging his hammer too early and then quickly charging again (similar to her younger sister's machine sit attack). The way to determine which tactic she will use (which is also extremely annoying to guess) is checking if her mouth opens straight or if it opens crooked with her waving her hand wildly. If she does the former one she will do a straight ram. If she does the latter she will stop for a second then continue. In the Japanese and European version of the game, every time after the player attacked Princess Shoob, a ! appears above her and she would charge at the brother who attacked her, no matter whose turn it is.
Once she loses 3500 HP, she activates her crown and morphs into a hideous beast, which is her true form, and causes Princess Peach to faint. 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. The leg tentacles and crown come back in about three turns after their health is depleted and each arm tentacle comes back in one turn. 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 1 damage per strike. Once the crown is deactivated, Elder Princess Shroob's defense will significantly decrease.
Each body part has a different attack usually going in this order: feet or head; arms; then feet again which is always the tentacle sweep move. This move that can be dodged by jumping is eerily similar to Cackletta's arm swing attack in her ghost form. Once she has taken a certain amount of damage, she will use three tentacles instead of two. The feet have three attacks in total and each one is synced with the head; one move is where the Shroob royalty backs up with her feet and then spits out poisonous clouds of gas like the one Swiggler uses but is dodged by jumping. Another is the one mentioned earlier, the tentacle sweep. The last is the rarest attack of them all; she backs up, summons a Time Hole and six saucers, and spits a giant laser ball that hits the saucers, causing them to either burn or decircuit and make them fall into the time hole, then she resumes her attacks. The next turn, if the legs aren't destroyed by then, the Time Hole is back and the saucers attack either Mario or Luigi. The burning ones attack Mario and the shocked ones attack Luigi which is a reference to Mario's Firebrand and Luigi's Thunderhand abilities from Mario & Luigi: Superstar Saga. They come in the order that the giant laser ball hits them, the first one the giant laser-ball hits is first, and the last the giant laser ball hits is the last.
Her head only has one attack; and that is summoning up a giant laser ball and hitting saucers with it identical to the time hole one except with out the time hole making it significantly easier. Her tentacles have three attacks that are quite awkward. One is to grab the brothers and throw them. The babies must hit the tentacles together repeatedly as they slither forward to prevent her from grabbing them. This attack can not hurt Princess Shroob in any way when countered. This needs both bottom tentacles to activate. Another attack is to shoot a huge laser ball into the air then throw red and green energy balls into it. The ball will fall towards the brother whose colors match the highest number of colored blasts that were absorbed by the orb. It can be countered solely with hammers. After the giant energy ball is countered by the targeted brother, it will fall towards the other one and must be knocked away again. This strike will send it straight into Princess Shroob's face, damaging her. This attack needs both top tentacles to activate. Finally, her last attack is to stab a brother with the tips of her tentacles. The tentacle will shine first before attacking. Each tentacle is assigned to a brother (right for Mario, left for Luigi). Her top right tentacle hits above Mario and is only used when there is no top left tentacle. The top left tentacle hits above Luigi and is only used when there is no top right. Also this attack is only used if both bottom tentacles are present.
When the player finally beats her, Baby Luigi claims her defeated Shroob Mushroom form. The party returns 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 is then awakened and transformed into "Shrowser" and the brothers must battle him. Shrowser is easily defeated. Princess Shroob's ghost explodes while Bowser goes back to being unconscious. The game then ends with the babies and Toadsworth the Younger finally returning to the past.
 Mario & Luigi: Bowser's Inside Story
Bizarrely, Elder Princess Shroob was one of many Shroobs seen in cold room in the bowels of Bowser's Castle during Mario and Luigi's fight with the Shroobs in Mario & Luigi: Bowser's Inside Story, implying that she managed to survive the events of previous game but was frozen to prevent her evil plans from continuing, or that her body is simply being preserved. How she could have not only survived but regained her original form is unknown. The truth behind her appearance remains a mystery (and is decidedly left thus by Nintendo), though it is notable that she only appears in the background of the battle, as do duplicate Junior Shrooboids and Commander Shroobs; outside the battle, the only Shroob (aside from the three Mario and Luigi fight) that can be seen is one Junior Shrooboid, and the room is much smaller than in the battle.
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 concern at all for her own people. Whenever a Shroob UFO performs a task for her, she knocks it away, 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.