Poseidon wasn't going to hold the shape of a stallion much longer, he could feel the power shifting inside of him. It was the energy she was giving off, the proximity of her body, and the fact that she had ridden and controlled him so easily. She was almost certainly a goddess of the hunt or animals. It was like she was attuned to his body as a stallion.
Her touch was calm, he inhaled sharply and let the change happen. His eyes closed tightly as he focused on Jeremiah and the mortal form. The first time he had tried to change back, he had been stuck. For hours as a horse. It was easier as time passed. The years he had been trying giving him the ability to do it within minutes.
A long minute ticked by as Poseidon changed his forms and stared down at the tiny woman standing so close to him. "Poseidon." He growled as he grabbed her around the waist and against his very naked chest. Shapeshifting did not allow for clothes to be worn and he was as bare as the day Jeremiah had been born. He kissed her roughly, without permission and without warning. It was swift and short before he broke the contact and took a step back. "And who are you to jump onto my back as if you belonged?"