Bonetail

Bonetail is a large zombified Dragon in Paper Mario: The Thousand-Year Door, living at the bottom of the Pit of 100 Trials.

He is the oldest member of the "tail" family, older than both Gloomtail and Hooktail. As his name implies, he is merely a skeleton of a Dragon, implying that he has been living far longer than the other members of the family. He was once a pet of the Shadow Queen and was put in the pit to guard and punish anyone she wanted. The reason why he became a skeleton is that he never ate anything for so long and died of old age. Any actions outside of the Pit of 100 Trials, if any, are unknown.

After Mario and his teammates reach the bottom floor of the Pit of 100 Trials, Bonetail will roar, making it questionable if he can talk, as he has not ever demonstrated that ability. Bonetail's many breaths can confuse and cause sleep. He can also restore his HP if it's low. Eventually, Mario defeated him and Bonetail burped up a chest containing the Return Postage Badge.

Bonetail is the strongest enemy in the game, even stronger than the Shadow Queen. He is not necessarily harder than the Shadow Queen though, because the Shadow Queen has two hands, which can allow her to attack more than once, however the player may prepare however they wish for the Shadow Queen battle, but they may be exhausted from completing the previous 99 levels of the Pit of 100 Trials before reaching Bonetail.

Trivia

 * In the German version of Paper Mario: The Thousand-Year Door, Bonetail is portrayed as female.
 * Bonetail plays the same role in this game as The Master (in his final form) did in the original Paper Mario, in that they are both completely optional and stronger than the final bosses from their respective games.