Well, shoot. I had already depicted a shark hybrid, back when I could've chosen any fish.
Approaching this one, the working plan was to depict a different kind of shark, like maybe a manta ray.
But researching "Polymorph" unearthed, in addition to being a D&D spell, (And not a creature as I'd hoped,) that Polymorph is also the British name for a heat-moldable plastic sculpting material.
The picture ended up going in a very different direction from there.
Completed on-time, within one day.