This one left me more confused, since I guess it left out stuff from the novels.SpoilerI'm not convinced Echidna is the evil one, especially since the other witches are also on friendly terms with her. As for the Ryuzu experiments, it just seems like a lot of witches made stuff for the hell of it. Like Gluttony with the White Whale and Vorpal Bunnies. I thought they might be connected, like the clones are the bunnies, and they eat to make more Ryuzu clones, but that totally doesn't make sense if you believe why Gluttony made the bunnies. I also didn't go back to look, but Satella looked like she has a black flower in bloom where Emilia's white flower bud is.
I don't think Subaru would've promised to save Satella after stabbing himself at the beginning when he was surrounded by shadow. That was Emilia. He was also scared of her afterwards when he restarted. As for the other witches, it could just be that Echidna is the most powerful of them and has control over the construct. Those witches are weird as hell. It's hard to say if logic applies to all of them. Greed seems the most straightforward. I think we'll get a nice lore dump next episode that will answer a good chunk of questions/theories.