Nue Houjuu has the ability to cause misidentification. I just noticed that not just some things, but just about all things about her are (copied from/stolen from/taken from/pieces of, you choose the word) other characters. Let me elaborate;
her appearance:
Snake like Sanae
unusual wings like Flandre
Gothic-Lolita like several other characters
many people have said that her theme sounds a lot like Flandre's theme or Mystia's theme (UN Owen was her and Deaf to all but the song, respectively) just look at the comments on the Heian Alien videos:
http://www.youtube.com/watch?v=JMXaJvxGAxo (first youtube video to come out from youtube when searching "Heian Alien")
and then there's the actual fight. There's a lot about this.
this is the fight against her btw:
http://www.youtube.com/watch?v=t-LHKCXTXFIthe very first danmaku she fires in an Lemniscape pattern.
I was playing Touhou 7 on normal when I saw that Chen's last spellcard has the same pattern
http://www.youtube.com/watch?v=9q0Z9ZovCP0 3:47
then her first spellcard begins. She uses dark clouds and razor lazor beams. For the dark clouds, I was thinking Mystia's 2nd and 3rd spellcards:
http://www.youtube.com/watch?v=xgNnl35wFn0 2:10
the razor lazors remind me of Koishi's 1st spellcard, which in itself is just like Kanako's first spellcard
http://www.youtube.com/watch?v=pnxTVPTE1PQ 0:14
though other bosses do this too, namely, Satori Komeiji
http://www.youtube.com/watch?v=iSPGuVxhrqA 1:00
She then goes back to firing her Lemniscape danmaku.
then her 2nd spellcard begins. it's a spiral pattern that homes in on you, which so many bosses do in part or in whole... (Note how the creator of the video says in the annotations "I know I had seen this kind of pattern, but I just can't tell where")
the next thing she does is fire danmaku in all directions (circularly) and the point at which it is fired moves in a counter-clockwise circular fashion. Again, many bosses do this in part or in whole.
her 3rd spellcard is wavy danmaku fired in all directions. Again, the maker of the video says "Can't really pinpoint this one. I'm sure there's a lot of circular attacks like it"
Yuyuko's 1st spellcard
http://www.youtube.com/watch?v=Fsp0ESbQoCs 1:38
*suddenly gets tired of making youtube URLs*
The next thing she does is the same as what her last non-spellcard attack was, except a second firing point mirrors the first on the other end of the circle they are moving on
video maker says "hey, this is kanako's..."
spellcard 4: more razor lazors.
next attack: more Lemniscape. the maker of the video then says "Where have I seen this pattern before this boss? Reimu? Seihou?"
her 5th spellcard. Razor Lazors (I refer to them as that because they have a razory shape btw) which turn into regular danmaku and back
as the maker of the video says: "Ooh, ooh, I know this one. Shou"
then she makes falling orbs. the maker of the video calls them "mini suns". *coughcoughutsuhoreiujicough*
then she has green lazors and smaller dual yellow lazors spiraling around each one.
"OK... uh... Shou or Byakuren, not sure"
more mini suns~
she then makes more dark clouds for her 7th spellcard
"Ran and Yukari, no contest"
she then pulls out some very overused red orbs. See Yukari, Remilia, Utsuho, Patchouli, etc.
then Hina with the rainbow UFOs.
then comes her survival spell card.
Flandre's kagome kagome and Koishi's 2nd to last (a survival) spellcard
and her final spellcard is more razor lazors becoming normal danmaku.