Which of Ovid's works deals with transformations?

The work that deals with transformations by Ovid is "Metamorphoses." This epic poem is famously structured around the theme of change and transformation, narrating numerous myths and stories that explore how characters undergo physical changes or transformations into different forms, such as animals or plants. The narrative weaves together a vast array of myths, showcasing Ovid's creativity and his fascination with the concept of metamorphosis, making it a defining work in the genre of mythology.

In contrast, "Heroides" is a collection of letters written by heroines from mythology, expressing their feelings of love, longing, and betrayal, which does not primarily focus on transformation. "Ars Amatoria" is a didactic poem that offers advice on love and seduction rather than dealing with literal transformations. "Medea" is a tragedy that tells the story of the character Medea, focusing more on her actions and emotions rather than on transformations as a central theme. Thus, "Metamorphoses" stands out as the work that directly and extensively addresses the theme of transformation.