A poet celebrated for his syncretism, Shelley’s sense of fluidity arguably extends to his understanding of sex and sexuality, as he wrote during a time of peak flexibility and transition in thinking about gender-sex. Reading Erasmus Darwin’s descriptions of variously sexed plants, Ovid’s tales of shapeshifting, and William Lawrence’s intertwinement of sexed and racialised bodies, Shelley, the great poet of relation, comes to see the body as materially shifting, porous, and relational. Reading passages from A Discourse on the Manners of the Ancient Greeks Relative to the Subject of Love alongside the figure of nonbinary, intersex creation in ‘The Witch of Atlas’, Asia’s transformation into the posthuman ‘lamp of light’, and the nonhuman ‘shape all light’ in ‘The Triumph of Life’, this essay suggests Shelley began to understand polymorphous sexuality connected to sexed bodies of shapeshifting, mutable morphology.