Sentinel

Sentinels are strange, flying enemies that appear in Paper Mario.

History
Sentinels are found throughout Tubba Blubba's Castle where they are tasked to throw out any intruder that enters the castle. When a Sentinel spots an intruder, they will quickly hover over the person and slowly lower onto them and grab them with their "claws." The Sentinel will then toss the intruder out of the castle. The only way to avoid being captured by a Sentinel is to use Lady Bow's Outta Sight techique when a Sentinel closes in.

During the events of Chapter 3, after Tubba Blubba finds out Mario is in his castle, he crashes through the floor crushing the Sentinels in the main room in the process. After Tubba Blubba is defeated, all of the Sentinels are gone from the castle proving they were working for Tubba Blubba and, by extension, Bowser.

Trivia

 * Sentinels are one of very few enemies in the game that aren't encountered in battle.