My reference belongs to the fact that the bosses may go through one wall and then appear on the other side. I'm not sure if I remember it right but I think that it's possible with top and bottom as well. That's why portals came into my mind.
Speaking of whitch maybe you could add those? Though I have no Idea about it I don't think that'd be too difficult.
Now that you mentioned Touhou (at least I assume you mean that) I've never played it myself but I watched the final boss recently and it was kinda funny to see how the worst you can get from a difficult pattern in WAKER is the easiest in that fight. Anyway, how does that timer work exactly? I'm not sure how a useful implementation would look like.