Like they were going for a Cave style mode in Mystical Power Plant before but I think they nailed it pretty good this time.
Stage and boss design are quite amazing and the constant hyper mechanic reminds me a lot of Crimzon Clover Boost. All of the masses of extra enemies to balance it also makes it incredibly fun.
The thing I noticed is that usually in games with these kinds of bosses, you wait for a certain pattern to get a really good bullet clear - but in this game there's no incentive to do that; you just want to power through spell cards as quickly as possible.
Stage 3 does not exist. I mean come on they didn't bother to update Ruri's sprite for Phantasm :V
There are several Overdrive spells that are unused at this time. Given that the devs threw out two patches yesterday I think it's safe to say that another update is forthcoming.
Kiyohime's survival spell is every bit as awful as everyone's saying it is. If you memorize the first two waves (bottom left corner until the red familiars re-aim, top left corner until the orange familiars re-aim) that's may get you far enough in that you won't have to bomb too too much? I have a video showing a route for the whole thing but I don't even expect
myself to remember all that fourteen minutes into a run. Also, though this probably doesn't need to be said, don't use hypers.