Alastor Boo The 2nd, or just Alastor Jr., is the youngest Booling and favorite son to King Boo. He is much like Bowser Jr., as he looks just like his father. He is best friends with Bowser Jr. as well.
He is constantly bullied by Roy Koopa, Bowser Jr.'s older brother. He always tries to be like the other Koopa Kids, but usually ends up get beaten by Roy.
He supports almost all of his father's plans, much like the Dark Moon Incident. He recently appeared in Super Waluigi! as the most-faced boss in the game. Since then, he has held a grudge for both Luigi and Waluigi.
He is the size of a normal Boo, which a few differences. Much like Prince Boo, he wears a giant version of his father's crown and has a white pacifier, which leads to people confusing him with Prince Boo.
He appears as the Spooky Manor boss in the game 3 times. The first time, he introduces himself to Waluigi, and uses his tongue as a hammer-like weapon. If you beat him, he falls to floor, starts crying, and runs away from the scene.
The second time, he comes and shows you his tongue, which has a few bandages around it. Now, instead of using his tongue, he uses his crown as a boomerang, and tries to hit Waluigi. If Waluigi kicks the crown at Alastor 3 times, he falls, and once again cries for his father.
The final battle with him is before the final level. This time, he stammers whenever he looks at Waluigi, with a look of immense fear of his face. Now, he uses a magical rattle, which sends blue and green fireballs at Waluigi. If you jump on him 3 times, he falls to the floor, crying and admitting his fear for the purple plumber. In the end, he is seen being hugged by his bruise-covered father, still crying.
In the sequel to Super Waluigi!, Alastor Jr. appears as a boss, taking control of Scary Sky. He is still scared of Waluigi, as he whimpers whenever Waluigi runs or attacks. He uses his tongue, his crown, and his rattle as his attacks once again. If you stomp on his tongue 3 times, he'll moan in pain, cry, and run to tell his dad about Waluigi.
In the credits, he is seen welding something with a torch, revealing that a prequel could probably come out.
- In Super Waluigi!, it is revealed that he has sensitive feelings, which he only shows to Waluigi, Luigi, and Bowser Jr.