Jr. Troopa

 is a boss in Paper Mario.

He reappears in the game a few times and has some pretty difficult fights.

Goomba Village
When Mario and Goompa are looking for the Hammer, Mario finds himself in Jr. Troopa's playground. On the way out, the fiend appears and begins to wonder why they've entered his home. He battles Mario in anger. This battle is nearly fixed so that Mario can't lose, but Jr. Troopa tries and nearly defeats Mario. After beating him, Jr. Troopa runs off, sad and angry.

Pleasant Path
On the way back to Toad Town, from Koopa Bros. Fortress, Mario finds Jr. Troopa yet again the two square off. Jr. Troopa shows off his new found ability to not only swim, but to hide in his shell as well. With the new-found abilities and partners, Mario defeats him with ease.

Forever Forest
After just entering the Forever Forest, Mario and his partners hear some loud yelling. Upon a closer inspection of the forest, they run into Jr. Troopa again. Excited, he attacks Mario and two battle for the third time. After beating him, Mario see him run off into the forest. After making his own way through, Mario notices Jr. Troopa run off to Toad Town.

Toad Town
A little later in the game, Jr. Troopa goes after Mario to Lavalava Island. He swims to get to the island, but unfortunately, barely misses Mario. Afterward, he swims back to Toad Town in pursuit. He eventually makes it there and attacks Mario. The two square off yet again, but Mario still prevails, as Jr. Troopa lost a lot of his stamina while swimming to Lavalava Island and back.

Shiver Snowfield
As the game progresses, Mario eventually is confronted by Jr. Troopa once again. The koopa finally tracks Mario down and challenges him for the fifth time. Jr. Troopa, now armed with his powerful Magic Wand, think he can finally defeat him, but fails. Mario leaves the area on his quest to the Crystal Palace and leaves. On the way through the area, until the completion of Chapter 7, Jr. Troopa remains in a frozen block.

Bowser's Castle
On the way up through Bowser's Castle, Mario faces many hardships, but none come close to the final room of the castle. Mario is confronted by the final Bowser Door and must end up fighting the Koopa Bros.. However, Jr. Troopa walks into the run and knocks out all four of the koopas. Then, he battles Mario in the final show down. After losing, he knows he is bested and runs off. The door then becomes confused and doesn't know if he should let Mario through. Believing that Bowser can't be beaten by Mario, he lets him through.