Koops is first encountered in the town of Petalburg during Paper Mario: The Thousand-Year Door. Being the son of an adventurer, his father went off to kill the dragon Hooktail and never came back. At first, Koops is a timid and shy Koopa who barely talks to Mario. As Mario prepares to confront Hooktail, Koops offers to join Mario to avenge his father. After Hooktail is defeated, Koops finds that his father Koopley had been living inside of Hooktail's stomach along with the Crystal Star for the past several years. Even after finding his father, Koops remains with Mario for the rest of the journey. In the field, Koops can jump into his shell as Mario kicks him. Koops will spin away for a short distance, then come back. This can be used to attack enemies or grab hard to reach items. The player can even hold down the button to keep Koops frozen at a position, spinning away. In battle, Koops can hit enemies by flying towards them in his shell.