One other thing I noticed in this poster is that the IMAX part is covered with thorny rose vines, which previously were used with Gertrud the Rose Witch. It could just be a stylistic thing, but combined with the all the witch cards from the original series, it reminded me of my theory that Walpurgisnacht will have a different power set in this movie once her true nature (origins) are revealed, and it will involve using powers and abilities from all of the witches and/or their familiars that were in the Law of Cycles.
You may recall that familiars from the witches in the original series all had cameos in Rebellion during the Homulilly battle, the idea being that all of these other beings in the Law of Cycles were "sending their support" to the fight, which, among other things, is why Sayaka was using "rental" versions of Gertrud's puffball familiars. If Walpurgisnacht is truly the "inverse" of the Law of Cycles and made from its component parts (i.e., the witches previously in the Law of Cycles), it would be a fascinating callback if the reverse happened in the new movie, with all the witches/familiars now fighting on the "wrong" side. I'd love to see what these "dark rentals" might look like, and it sounds exactly like the sort of thing Doroinu Curry would have fun designing. But TBD.
Also, this poster appears to answer a different question that I had - if there are 2 versions of Homura, the original and the mirror image, does the mirror image also have a lizard? - and the answer appears to be "no". The lizard is the original Homura's symbol and the embodiment of her power, so it makes sense that the double wouldn't have it (though I confess I'd enjoy seeing the "dark"/corrupted version, lol). On the double's side, there's just empty space - or, if you prefer, a spiral.
Which is exactly what the double's symbol is in the trailers, by the way: a spiral galaxy with a diamond-shaped black hole at its center.
Lizard vs. spiral - the ultimate match-up.
There are other spirals associated with the doppelganger - the staircase, the barber poles, etc - but this is the most obvious in my book.
And while both versions of Homura are the result of this "spiral" motion through time, the spirals in this poster are also mirror images of each other - the same shape moving in different directions. Which is also symbolic, of course. The original is moving counterclockwise (against time) and the other is moving clockwise (with time).
In keeping with the botanical motif, these spirals also remind me of fiddlehead ferns uncoiling, although @bernkastel11 pointed out they also look like fan blades if you focus on the negative space.
Earlier on my dash this evening, someone reblogged a bunch of illuminated manuscripts with elaborate golden borders and the resemblance is striking. I also really love how it looks like Walpurgisnacht is leaping from the pages of a book out into reality, which is more or less what's going to happen in the movie given that the books in question are floating around her in this image.