"Between two forms, and an addition"

As Lenn worked on transforming himself into his feral form one day, he moved too much in the very last moment... And his interrupted transformation had a much different result than normal. He ended up partway between both forms - keeping his arms while his legs fused into his tail - but he quickly noticed something else had happened: Somehow, his transformation going weird had turned him female! She inspected this odd new form... And figured she could spend some time in it, fashioning a makeshift bra out of some seaweed.

When she eventually wanted to go back to land, she started changing back to being anthro, accepting that she might become a guy again... Sure enough, Lenn went back to being himself at that point. But, all that had been so interesting that he decided he'd try to figure out how to intentionally take on that form.