Gloomtail

"WHAAAAAAAAAAAAAAAAT?!? You destroyed my precious younger sister?!? I wondered why she hadn't written recently... Quake in fear, mortals! For I am Gloomtail! I will avenge my sister by taking your lives...and then gnawing on your bones!"

- Gloomtail

Gloomtail is the middle sibling in the "tail" family in Paper Mario: The Thousand-Year Door. He is the older brother of Hooktail and the younger brother of Bonetail. Upon hearing Mario's partners say they defeated his sister Hooktail, Gloomtail vows to destroy Mario and company and avenge his sister. He lives in the Palace of Shadow and guards the Star Key, which is needed to unlock the pedestals in the Riddle Tower. Mario and company had to defeat Gloomtail to get the Star Key.

Gloomtail is stronger than his sister. He attacks by breathing poison on Mario and his partner (taking at least ten turns to wear off), and stomping or chomping the character in front. His Earthquake move can be dangerous, but it doesn't work on Vivian and Flurrie. He can also charge up for his signature and strongest attack: his Megabreath move, which does up to 16 damage.

Quotes
For a full list of quotes, see here.

Trivia

 * Out of all of the siblings in the "tail" family in Paper Mario: The Thousand-Year Door, Gloomtail is the only one not to have a Super Paper Mario equivalent.
 * The room Sir Grodus is fought in is directly below Gloomtail's room, which would mean that Bowser was in Gloomtail's room when he fell through the floor. In fact, if the player uses cheats or glitches to go to the hidden area behind Gloomtail's room after defeating the Shadow Queen, a large hole can be seen. The hole can be jumped down to enter the aforementioned Grodus room.
 * Bonetail has the same default attack and defense stats as Gloomtail.
 * If Mario brings Flurrie, Yoshi, Vivian, Ms. Mowz, or Bobbery when seeing Gloomtail—partners that were not available during the battle with Hooktail—they will confuse him for Hooktail, going off on several descriptions Mario told them about offscreen.