Gloomtail

"Quake in fear, mortals! For I am Gloomtail!"

- 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. 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 much stronger than his sister. He attacks by breathing poison on Mario and his partner and stomping and chomping the character in front. His Earthquake move can hit hard, but it doesn't work on Vivian and Flurrie. He can also charge up for his signature and strongest attack: his famous Megabreath move, which does up to 16 damage.

Quote
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Trivia

 * As with his sister, Gloomtail bears a slight resemblance to the Czar Dragon.
 * Gloomtail is the only dragon boss in Paper Mario: The Thousand-Year Door that does not have a Super Paper Mario equivalent.
 * The room Grodus is fought in is directly below Gloomtail's room. Which would also mean that Bowser was in Gloomtail's room when he fell through the floor.
 * Gloomtail acts similar to the Elder Princess Shroob, both are merciless and want to get revenge for their sisters that Mario defeated.