The Corpse Party: Book of Shadows (Blu-ray release 2017-1-11) follows directly from the original movie. One of the survivors has a sister, who happen to know many secrets about the school in the alternate dimension, happen to be able open an inter-dimensional hole to go there, happen to be able to incant something that drive monsters away, and happen to have an actual bone of the little girl who created the whole curse.
The survivors decide to use the bone to go back to the school and travel back in time in the hope of saving everyone. Since this is a slasher horror movie, it would not be a spoiler to say that all this means is that we get to watch the people die again, at slightly different times and in slightly different and less interesting manners. If this sounds dull, yes it is. So the movie adds two new antagonists – the major one is far less fearsome than those in the previous movie, the other one should be more powerful but have little screen time.
In spite of the Book of Shadows being in the title of the movie, its subplot does not begin until near the end of the movie. I can only say this subplot is as much a disappointment as the rest of the movie is. Although the previous movie had a relatively rich story, the new elements introduced in the sequel are just senseless. The movie also inserts shots of fake gore that have no relation to the plot.