Download the english version of Shimeji here:
https://code.google.com/p/shimeji-ee/
The "mischievous" version will allow Shimeji to clone himself and mess with your web browser. The "calm" version will disable this.
Get the Asriel Shimeji skin here:
https://www.dropbox.com/sh/lgjhmd1f53ityzc/AABzq7DH7sxGAUfmG3xJZREna/Shimeji?dl=0
Add these files to their own folder inside the img folder.
Then just run the program, and you'll have your own desktop Asriel. Toss him around, or just let him climb around and be cute.
And yeah, original tumblr post here
http://pkbunny.tumblr.com/post/133700641604/here-is-your-little-goat