Elder Shrooboid

The Elder Shrooboid is a boss in Mario & Luigi: Partners in Time. He acts as the Boss of the Star Shrine and is the holder of the fifth Cobalt Star shard. It is a red Shroob with yellow spots and spikes on top of its head. It is the strongest of all the Shrooboids. Mario, Luigi, Baby Mario and Baby Luigi must fight this powerful Shroob at the Star Shrine high above the Mushroom Kingdom. Before the battle, the Elder Shrooboid will incapacitate Toadbert and Kylie Koopa, and steal the Toad's Cobalt Star shard. When the Mario Bros. arrive at the top of the shrine, Toadbert made an attempt to reveal the truth of the Cobalt Star and the Elder Princess Shroob trapped inside by having Mario rub off the dirt on his strange sketch that he had made awhile beforehand, revealing two Princesses. He and Kylie Koopa, were then turned into purple Shroob Mushrooms by the Elder Shrooboid. Hoping to gather all the shards and awaken its leader, the Elder Shrooboid attacked the Mario Bros.

Battle
When the Mario Bros. and their past selves battle the Elder Shrooboid, he will use a variety of attacks against them. First, the Elder Shrooboid will trap Mario and Luigi in crystals (like the Shroids) and will run off and grab a heavy metallic ball on a chain. Mario and Luigi must jump to break their crystal imprisonments while the Elder Shrooboid spins the ball and chain towards them. The spinning will then cause the Shrooboid to become dizzy, he will then drop the metallic ball and fall down. However, the Elder Shrooboid will get up again, scream in rage, and knock the ball into either Mario Bro. then lunge head first into the other Mario Bro. The metallic ball will either have an "M" (for Mario) or an "L" (for Luigi) marked on it, showing which Bro. the ball would be used against. As such, the appropriate Mario Bro. must to jump over the metallic ball while the other one had to jump over the lunging Shrooboid. If the Mario Bros. cannot break their crystal prison quick enough, they will not be able to avoid the Elder Shrooboid's attack.

Like the Junior Shrooboid, the Elder Shrooboid can also perform a spin attack against Mario or Luigi. The corresponding Baby Bro. could counter this attack with a their Hammers. However, the Elder Shrooboid will keep coming back, meaning the Baby Bro. must counter multiple times. The Elder Shrooboid could also shoot fireballs (like the Blazing Shroobs) from its hands at the Mario Bros. He may shoot two fireballs at once. Mario and Luigi must jump to dodge these fireballs. As such, Baby Mario and Baby Luigi had to use their Hammers to deliver damage to the Elder Shrooboid. though, if either Bro tries to jump on the Elder Shrooboid, the spikes on his head will damage them, which limits the types of items they use.

The Elder Shrooboid also can create a spiked ball that it would throw towards a Mario Bro. The ball will circle around the bros until it closes on one of them and strikes them. It moves faster and faster after each orbit. If hit, the Bro. will be damaged and possibly poisoned. The ball can be deflected by a Hammer strike from Baby Mario or Baby Luigi, sending the spiked weapon flying off into the air. Deflecting this attack, the Elder Shrooboid will gasp and fall over from shock. When on the ground, the Elder Shrooboid will become vulnerable to jump attacks, and any attack would do more damage than usual.

After many hits, the Elder Shrooboid started to shrink into nothingness. Surprisingly, the Elder Shrooboid instantly grew to  to humongous proportions. When in this state, the Elder Shrooboid had the same attacks as before, but the attacks were faster, more powerful, and giant-sized to fit his new body. Additionally, after becoming gigantic, the Elder Shrooboid will release a Shroob UFO from its mouth. This UFO holds a sign with the number four on it, indicating to the Mario Bros. that they only have four turns left to defeat the Elder Shrooboid. If they can't defeat the monster in four more turns, the Shroob UFO would fire a massive energy blast that will KO all four of them. The Mario Bros. can deflect the Elder Shrooboid's spiked balls at the Shroob UFO, and can reset the counter back to four turns. When Baby Mario deflects a spiked ball, the weapon will fly above the Elder Shrooboid, but if Baby Luigi deflects the ball, the spiked weapon would fly above the Mario Bros. Since the Shroob UFO changed positions in the air during the battle, only one of the Baby Bros. can deflect the weapon to reset the counter. If the UFO is above the Elder Shrooboid, Baby Mario must deflect the spiked ball. If above the four Mario Bros., Baby Luigi has to deflect the spiked ball.

In the Japanese version, the spiked ball always goes up, even if Baby Mario deflects the attack. As such, the Shroob UFO will stay above the Mario Bros. making it much easier to hit in the Japanese version.

After a long battle, the four Mario Bros. will defeat the Elder Shrooboid and recover the fifth Cobalt Star shard. Although their friends were transformed into Shroob Mushrooms, the Bros. had to continue their fight against the Shroobs. With the fifth star shard, the Bros. can gain access to Shroob Castle. Leaving the Shroobified forms of Toadbert and Kylie Koopa behind, the four Mario Bros. must return to Peach's Castle in the future to prepare for their final campaign which is to enter Shroob Castle itself.

Trivia

 * Elder Shrooboid's coloration and its age to the Junior Shrooboid are analogous to Mario is to Luigi.
 * Elder Shrooboid has the third highest HP, with both phases totaling 2950 HP, 50 less than Princess Shroob with 3000 HP and 3550 less than both phases of the battle against the Elder Princess Shroob with 6500 HP total.