Hooktail Castle is a location that is found during the events of Paper Mario: The Thousand-Year Door in Chapter 1. Although not explicitly stated, it is the first major dungeon in the game, as it takes place in a closed location that features many traps and enemies, a boss at the end, and a quest reward at the end. It is the castle where Hooktail, the dragon who is terrorizing Petalburg, is fought and resides. Mario, and his partners — Goombella and Koops — travel here to defeat Hooktail and collect the Diamond Star. The castle is full of many traps and enemies that Mario and his partners must avoid and defeat. The enormous rooms in the castle provide a resting place for some of the Koopas that have fallen victim to Hooktail's ways — however, not all of the skeletons found throughout the castle remain in an eternal rest.
Though not much is known about the entire history of Hooktail Castle, some backstory was revealed throughout Paper Mario: The Thousand-Year Door in stories and rumors talked about amongst the many creatures Mario meets along his travels. According to some stories told by Grifty, Hooktail Castle was built long ago in order to harbor one of the Crystal Stars. Ironically, despite that Hooktail Castle was created to contain one of the Crystal Stars — which were scattered across the world in order to keep the Shadow Queen at rest — Hooktail was the guardian of the castle as well as one of the Shadow Queen's pets. It is unknown if the castle was originally created vacant, and then later taken over by Hooktail by purely coincidental means, if it was taken over by Hooktail purposely to guard the Crystal Star in hopes of somehow helping the long-dormant Shadow Queen, or if Hooktail was specifically put into the castle to guard the Crystal Star.
It is presumable that Hooktail Castle was once inhabited by beings other than Hooktail quite some time ago, as the castle features some torture devices including the Rack, a flail, and a ball-and-chain. Many of the rooms are filled with the corpses of Koopas, but it is unknown as to how long they were there. There were also some prison cells found in the castle, similar to those found in castles from fourteenth-century Spain and Scotland; one of these prison cells has the skeletal remains of a Koopa residing behind it.
 Paper Mario: The Thousand-Year Door
Mario and his partners enter Hooktail via a pipe that leads them into the background where the castle is structured. Upon first entering the castle, they find a Recovery Block and a spring that leads them to an Airplane Panel. Below the Airplane Panel is a broken bridge that hovers above a moat — at the end of this moat, they can also collect an HP Plus badge. As they soar across the moat, they reach a tall set of pink doors that lead them into the heart of the castle.
Immediately after entering this part of the castle, they encounter many Koopa Troopas and Koopa Paratroopas that are ready to attack. They can also find the Power Bounce badge within a red ? Block here. In the next room, they find many skeletons of Koopas that fell victim to Hooktail along their travels, including the remains of Kolorado's father. His skeleton is found clutching a note addressed to his son, Kolorado, as a warning about Hooktail and her weaknesses. The note contains his last words, as he wrote it while dying. In this note, Mario and his partner discover that they need to find something that begins with a 'cr' and ends with an 'icket' in order to defeat Hooktail.
At the far end of the room, they find a Red Bones guarding the doorway to the next room. As they awaken in, the room quickly becomes flooded with countless Dull Bones, which push Mario and his partner away from the door. After Mario uses his hammer to whack his way to the Red Bones, they engage in battle. Mario eventually wins, gaining access to the next room.
Through the next few rooms, Mario and his partner encounter many more Dull Bones in their path. After some travel, they eventually reach a room with a mysterious black chest. They quickly move to the room to the right and collect the Black Key. But as they attempt to make their way back, the entire floor becomes protruding with sharp spikes that form a maze throughout the room. To Mario and his partners' dismay, the ceiling, too, is covered in sharp spikes and is lowering quickly towards the ground, but the heroes escape the treacherous room and insert the black key into the chest. The demon that resides in the chest then curses Mario - from then on, he can turn paper thin and squeeze into even the narrowest of spaces. Mario and his partners makes their way back, collecting a red badge called Attack FX R. It is with this badge that Mario may have a chance at defeating Hooktail.
As Mario progressed farther and farther up the castle, he eventually entered a room and encountered a mysterious thief. The small mouse had come to the castle to steal rare badges, but was off before long. In that same room, Mario and his partners found they key to the room across the way. They unlocked the door and progressed furthermore up the castle. After going up two flights of stairs and traveling across the outside ledge of another room, Mario and his partners eventually reached a long bridge high in the air. This bridge was infested Koopas of different sorts along the way to an extremely high tower. At the top of this tower, Mario and his partners encountered a Save Block, Recovery Block, and an enormous pair of doors that led into a large circular dormitory. Through these doors, Mario and his partners encounter Hooktail. After a long battle, the dragon was defeated and regurgitates Koopley, Koops's long lost father. After a touching reunion, Koopley gave Mario the Diamond Star, something he had found in Hooktail's belly and had kept as a souvenir.
After Chapter 5, Merlon will be awaiting for Mario outside his shop in Rogueport. He tells Mario and his partners of a fortune he had received; this fortune told of a room hidden in Hooktail Castle. If Mario and his partners return to the room with the spikes and head to the far right of the room, they will discover a large crack in the wall. With the help of Admiral Bobbery, the wall was blasted way. In the secret room, they discovered the Up Arrow, an item that helped Merlon be able to power up Mario's partners even more.
 Enemies Found in Hooktail Castle
 Area Tattles
 Names in Other Languages