I looked it up and it is a group of editable Japanese mushrooms. mintyfoodfanpage.files.wordpress.com/2012/02/cogumelo-shimeji.jpg
It not like I am interested in half the thinks people look for or that a lot of what I need to look up is Japanese. I look thinks up and see people ask for American stuff that has a Japanese name. I can understand that because a long time ago everyone wanted to have an American Indian name. Mother that gave birth to a baby just name it after the first thing they saw. If it was winter their kids could be called Yellow Snow. So it is nothing as great as some people like to think. I think the same thing is happening with Japanese things, and names.
If you want to make mushrooms that is fine with me. You can learn a lot more if you look up Reishi Mushrooms. They grow in America but they are called a cure for everything.
You just download one of the shimejis first. It's got an engine with the file and there's a special image file with all the images like walk cycle or jump numbered in order. You just draw out the images and replace the old ones with your new shimeji movement images. If you just keep the same image name it should work for example if the original had a picture of someone jumping left and the picture was named image000.jpg you'd just make a new picture of someone else jumping left and switch it with the original one under the same image000.jpg name. Any art program works, they don't make engines for you usually to make new shimejis you just change it's appearance and keep the programming. I hope this was helpful. ^^