Spotted a video posted on another site that I thought it would be of interest to some people here.
Yang style 188 is the unofficial title for the video.
The Taiji player starts his 188 Form around the 9:12 mark.
about 8 1/2 minutes into the clip he says the form was created by Yang Banhou in conjunction with 2 of his friend based on their personal experiences and the exchange of techniques between the 3 of them. They just made up the form for their own practice, among friends, and so that's why it's never been broadly taught.
...which kind of fits with what I was saying earlier about how the forms didn't used to be so set in stone like they are today.
I have never heard of it; cannot verify it; just thought it would be interesting.