Monstar

Monstar is a ghost-like monster from Paper Mario that attacks those who enter Starborn Valley. When Mario and his friends first encounter it, Monstar appears tough to defeat. However, Monstar is really nothing more than a bunch of Star Kids trying to protect their home. When Monstar was about to attack, it would make a huge light show with amazing special effects. However, the attack deals only 1 damage point. After attacking, it asks Mario if he is scared yet in a shaky voice.

The battle was really simply moving the plot along than anything else, but Monstar still gives some Star Points.

Also notable about the battle is the fact that Monstar was invulnerable to Star Spirit attacks and the Shooting Star item.

Trivia

 * Its name is a pun on monster and a portmanteau of "monster" and "star".
 * Although he is one of the easiest bosses in the game, his attack is the hardest to guard (besides using badges and partner abilities) because the duration of the attack is very long and the player needs perfect timing for such a lengthy attack.