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.
This was to prevent the boss from getting stuck at the bottom, so they will warp to the opposite side :)
Speaking of whitch maybe you could add those? Though I have no Idea about it I don't think that'd be too difficult.
What do you mean?
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.
Touhou is very difficult (for me, at least), so I wanted to make something more accessible. Touhou also has a lot of variety in terms of boss attacks, many of which I am attempting to implement. However, Touhou can be difficult because it's handmade, while if I made WAKER difficult without any restrictions, the generated boss may be impossible to beat. I'm thinking of raising the side levels' difficulty though, since they are optional!
For the timer, think of it as the boss having poison. So every 1 second it loses 1% of it's health, and after 100 seconds it will kill itself from the poison. The values given are arbitary, but I hope you see what I meant :)