The 'extended' preview video for episode 12 is just more transformation clips:
http://www.vividred.net/next/12.html
Youtube version:
https://www.youtube.com/watch?v=KWJVtcZfqHU
But at least they did post some real preview screencaps for episode 12:
http://news.dengeki.com/elem/000/000/617/617301/