That's an interesting idea! You could start by adding a magical pumpkin patch somewhere in your story. Describe it as a mystical place where strange and magical pumpkins grow. The pumpkins have special properties, such as being able to transform when kissed. The pumpkin cat could appear from this pumpkin patch and kiss the main character, placing a seed in them. Over time, the seed starts to grow and the main character begins to transform into a pumpkin cat. As the transformation progresses, the cat gets bigger and grows, eating candy that appear in the main character's butt! The transformation eventually completes and the main character, now a fully-grown pumpkin cat, has magical powers. They can now use these powers to help their friends and go on grand adventures.