not actually a Shaolin form
If the legends are to be believed, Shaolin absorbed the bulk of its forms from external sources. Surely you've heard the old "sanctuary to political refugees" tale. What made Shaolin special was that it was a repository, or perhaps academy in the true monastic sense of the term, for the martial arts. Many of Shaolin's most famous forms probably originated elsewhere, but Shaolin incorporated them into their curriculum. They still do that today. It's part of the tradition of Shaolin. So when you say something is 'not actually a Shaolin form' I'm not sure what you mean.
Yinshougun is referenced as one of the five Shaolin staff forms in Shaolin's earliest extant manual, Cheng Zongyou's Exposition of the Original Shaolin Staff Method, which is dated at around 1610 CE. So it's been attributed to Shaolin for the last four centuries. It's also worthy of note that a major thrust of Cheng's book was to establish these five forms as authentic Shaolin staff forms. This was in reaction to a proliferation of non-Shaolin staff forms that bore the Shaolin moniker. Considering that this was an issue four centuries ago, that gives you some perspective on how old the discussion of 'what is authentic Shaolin and what isn't' is. It's been part of our tradition for at least twice the age of the United States of America.
I knew you were going to ask that next, Jingwu Man
Cheng lists five staff forms: yinshou, xiaoyecha, dayecha, pai and chuansuo. I've seen all but the last one demonstrated at Shaolin Temple at one time or another. I might have even seen chuansuo, but just not known it.
BTW, I'm currently learning a variation of yinshougun from Shi Yanfei. The latter half of his form is completely different than what most everyone is practicing nowadays. It's very interesting.
This variation is fairly traditional
There used to be three Shaolin representatives at our school (one has moved to another Shaolin school :rolleyes:) and they introduced a yinshougun to the curriculum which was fairly standard. Just recently, Yanfei busted out this different version which has a - dare I say? - almost more traditional feel than the standard. For instance, for Chop the Cudgel in a Lower Wing Stance (note I'm using the Shaolin Gong Fu – A Course in Traditional Forms lyrics since that's the most available in English) most practitioners do this flamboyant aerial backbend to slamming the staff on the floor pubu. It's the move we use for our Shaolin Staff hoody. I love that move. Anyway, Yanfei does it as this short sweep strike thing - a very practical, no-frills type of strike. He's done it that way a few times, very quickly. Most of the students are defaulting to the standard method - they haven't even noticed the variation. I've only seen him do it a few times so I haven't quite got it yet. He's not making a big thing of it all, almost like he's sneaking it out to see who's is fast enough of eye to see it. Or maybe I'm just tripping on a short cut he's using when he's teaching. Anyway, the other variations don't add anything that's not practical or overly flowery. Quite the opposite. I'm thoroughly enjoying the variation. It may be a keeper.