Am i the only one that feels sorry for mystia for being eaten?
Also i dont get it if yuyuko ate her why is she back for the later games

Well, see, Yuyuko was talking out of her ass for basically the entirety of IN's story, so you shouldn't really take her comment about eating Mystia any more seriously than you should her accusation that Kaguya froze the night (when Yuyuko actually did it herself). Or maybe it's just that the Border Team's scenario is the only canonical one that actually happened or something.