Junior Shrooboid

The Junior Shrooboid is a green monstrous Shroob who appeared in Mario & Luigi: Partners in Time. During the events of the game, this strange creature used Professor E. Gadd's time machine to travel from the past to the present. Eventually, Junior Shrooboid winds up in Princess Peach's throne room. Mario immediately confronts the alien (while Luigi runs away scared). In battle, the Junior Shrooboid has 13 HP and attacks by spinning into an opponent. Mario can Jump over this attack and stomp on the Junior Shrooboid in the process. After the battle, Professor E. Gadd places the Junior Shrooboid in a fluid tube, keeping the alien alive for study. E. Gadd discovers that the Junior Shrooboid reacts strongly while in the presence of the Cobalt Star shards. The professor hypothesizes that the Cobalt Star could be used to destroy the Shroobs, and commands Mario and Luigi to recover the remaining star shards. Unfortunately for the heroes, the Junior Shrooboid reacted so strongly not because the Cobalt Star could defeat the Shroobs, but because the Junior Shrooboid knew that it's leader was imprisoned inside the artifact itself.

Trivia

 * In Mario & Luigi: Bowser's Inside Story, while Mario and Luigi battle the Shroobs, eight Junior Shrooboids can be seen frozen in blocks of ice. Outside of the battle, one Junior Shrooboid is the only frozen Shroob that can be seen. Although two other ice blocks with unknown Shroobs were seen.
 * Junior Shrooboid is one of the two bosses fought in the present Mushroom Kingdom. The other is Shrowser.
 * Junior Shrooboid's color and its age to the Elder Shrooboid are analogous to Luigi is to Mario.