Jr. Troopa is a young Koopa Troopa still inside his little egg. He is a bully of the Goomba Village and is the first enemy where Mario earns star points. After getting beat up for the first time, Jr. Troopa swears to challenge Mario again. Jr. Troopa finds Mario again on Pleasant Path after he defeats the Koopa Bros. and rescues the first Star Spirit. During this battle, he encases himself in his egg and has more defense and power. Mario and his party members still beat him anyway. Later in the game (after getting lost in Forever Forest), Jr. Troopa once again fights Mario, this time with bat wings. He has a damage of five and is very hard to defeat. Despite his wings, Jr. Troopa still loses the battle and runs out the Forever Forest. The next time Jr. Troopa fights Mario is unfortunate for him. He has a spike on his head, wings, and immense power, but loses half of his health before the battle starts. Jr. Troopa narrow-mindedly swam to Lavalava Island and back, even though he could've used his wings. Had Jr. Troopa flown to the island, he might've beaten Mario at Toad Town Harbor. Once again....Jr. Troopa challenges Mario to a fight on the Shiver Field. Even though he has a large quantity of health, his only attack is a blasting magic at Mario. Mario and his friends manage to defeat him and Jr. Troopa is frozen in ice. (How he got out was never confirmed). The final time Mario confronts the adolescent bully is all the way on Bowser's castle in the sky. During this fight, Jr. Troopa changes into all the forms Mario has fought him once before. But none of it is enough to defeat Mario. Before running from the castle, he swears that the next time they meet, he won't be so lucky. Since then, Jr. Troopa has not been seen in the Paper Mario series (except for one minor appearance in Paper Mario: The Thousand-Year Door, where he appears in the background of Zip Toad's E-Mail).
He seems to be a stereotypical bully who takes whatever he wants, beats up anyone unfortunate enough to cross him or end up in his "territory", and is incredibly angry and short-tempered. According to Goombario, Jr. Troopa appears to be a blood knight, enjoying the thrill of a fight, and always trying to fight people stronger than himself, which Goombario considered an idiotic move. Upon first being beaten by the Mushroom Kingdom's hero Mario, Jr. Troopa became extremely angry and obsessed with getting revenge on the plumber and give him a massive beating that he will never forget.
His determination to kill Mario is so great, that upon discovering where Mario was, he would immediately rush to the plumber's location regardless of the obstacles and pick a fight with him, not stopping until Mario admitted he was a weakling. This one-track mind of his leads to him making rather short-sighted decisions. After Mario went to the Toad Town Harbor on a whale, Jr. Troopa, instead of using his newly-acquired wings to fly over the ocean, instead swam all the way to the docks, with his exhaustion leading to him losing half of his HP, which he himself admitted was a terrible move. He additionally does not seem to care about the situation of the Mushroom Kingdom (Bowser had lifted Princess Peach's castle up into the sky) or what Mario is doing at the moment, nor gives Mario the time to explain.
His hobbies include working out and ordering things by mail.
- Jr. Troopa can be optionally fought before going to battle against Tubba Blubba in Chapter 3. After Mario receives the Super Boots, he can decide to leave to the first area just outside of Boo's Mansion, and Jr. Troopa will appear.
- He can also be optionally fought right after Sushie joining the party in Chapter 5
- He is one of the few mini-bosses who keep trying to defeat Mario over and over in almost every chapter.