The Stage 4 Boss, Seiga Kaku, is a so called
wicked Hermit who can walk through walls(the anti-Kasen?). She is also the master of Yoshika and uses her frequently in combat.
I also think she's a ninja because she used the Kawarimi no Jutsu in her backstory.
The Stage 5 Midboss, Soga no Tojiko, is a ghost,
but her design looks more like Mima's than Yuyuko's. I also predict a lot of fanart of both her and Iku due to her ability to summon Thunder.
The Stage 5 Boss Mononobe no Futo has the ability to manipulate Feng Shui. That is roughly (and by that I mean "probably not at all") the same as Meiling's ability to manipulate Qi, but since she also has her leet martial arts that wouldn't be much of a problem. On the other hand, I can tell that Fandom will eventually see some sort of rivalry between her and both Komachi and Murasa since she also has a nice boat (that she rides on during some of her spellcards).
The Final Boss is Toyasatomimi no Miko. As if Gensokyo didn't have enough of those already. Japanese people might know her better as Prince Shotoku, aka the guy on the 10k Yen bills. She can hear ten people talking simultaneously. Sounds lame, until you find out that this allows her to hear people's
Ten Desires, and predict their past and future.
In the past the five of them have been manipulating a religious war between Shintoism and Buddhism in order to... actually I still have no idea what they were trying to do, except that they are all actually Taoists and are miffed over the fact that Hijiri built a Bhuddist temple over Miko's grave and delayed her resurrection. Or something.
She is also right-handed.In the Extra Stage, another UFO character makes her comeback. Nue, trying to help Hijiri against the Taoists, calls on an old friend from outside Gensokyo, the Tanuki Mamizou Futatsuiwa. Luckily she's a girl so she doesn't have some of the...
notable traits of a tanuki. However her last name can be translated as "Two Stones", so theres that. She has the ability to transform things (including herself), and is the first Meganekko since... Rikako I think? I think Gensokyo has a distinct lack of glassmakers. Zun also hints at a possible conflict between her and
the Foxes of Gensokyo.
I also have no idea why the two of them would fight the heroines if they actually, ya know, fought against their common enemies.