Not a Transformers, but have a look at the Chokogin Hatsune Miku X Rody. It's a nendo Miku who turn into a donkey thing. Lots of fun but the transformation almost triggered my inner TF nerd. She require BOTH partforming AND Shellforming.
Is there any official Transformers appart Beast Wars that have such a "triggering" transformation?
Have a review just in case:
https://www.youtube.com/watch?v=j2jk0pCjAWI 