Currently reading about a woman who turns into a dog at night (nightbitch). Unfortunately it's turning into a social commentary - I was totally not expecting this twist!

I was hoping for something along the lines of Metamorphosis, but with a dog instead of a cockroach (if only Ogtha existed in that universe)

I would even be content with a man turning into his own stalker

Or even turning into his wife, and then giving birth to himself

But the best transformations are when people become immaterial concepts

Eg: MC becomes horny