Ok... so I seen episode 21. It was the raw though.. So since I have no idea what was actually said, I'm going to explain as much as I did understand. Since it's a really big spoiler I might as well break it up into what it did answer.
1) What happened to Satoko?
2) What happened to Mion?
3) What happened to Keiichi?
4) What happened to Shion?
5) What was with the freaky ending on episode 8?
So, what did they show? Quitea few things. You see what happened to Satoko. I'm merely assuming that the talk her and Shion had before she stabbed her to death was about Satoko's relationship with Satoshi. Shion comes to her senses realizing she just killed Satoshi's sister, literally wetting herself at the thought. Doesn't last long though, and she resumes the lunacy.
They also explained what Oishi said about finding Mion in the bottom of the pit. After Shion zapped Keiichi, she went back to Mion and swapped clothes with her. Shion then tazered Mion and sent her down the pit too, putting her in the right place.
I'm guessing she really did go crazy. They sent Shion and Keiichi to the hospital and that night Shion went crazy, yet again.. ..marched over to Keiichi's house and.. stabbed him with the butcher knife. Yeah, you all remembered that part.
After Shion stabbed Keiichi, she snuck back to her room but she got snagged on something, slipped, fell, said sorry to Satoshi as the editors were nice enough to give her a slow motion drop... but then there was a budget cut in special effects and she fell instantly. NOt even a fade to black. So it was really SHION that was on the ground at the hospital!
Episode 21 ends with Shion falling. However, there's one thing that wasn't "explained". You all remember Oishi leaving Keiichi's room at the end of episode 8 and Mion popping out from under the bed, right? Well.. guess what? It IS Mion! Shion's died so there's no way it would be her. And remember, Shion and Mion exchanged clothes so, of course, she'd still be in the robe. Oishi said they found Mion in the pit. My guess is, she wasn't really dead. That's why they took her to the hospital. So, there are two ways it could've worked. the first would be the Natural Way, meaning Oyashiro isn't real and that it's just people doing all the work. Mion was pissed because none of this would've happened if Keiichi would've just given her the doll. Or even better, never came at all. So, she snuck into his room, under his bed, and waited until the last moment.. then I guess whatever went down there went down. But I think it's kinda impossible for her to kill him without people coming in and getting her...
Of course, number 5 is all just my good assumption.. but with great evidence.