To start, i think it is best to talk about the structure of the sprites in general, I would provide links and images but i just made my account after seeing this post.
The tool I am using is Tinke.
All Pokémon sprites are in a/0/0/4. This contains a lot of different parts for the sprites. For better use, we will skip the first 19 files as those contain data for a filler slot, when the Pokémon data is missing.
4_20.bin contains a static front sprite for Bulbasaur. This is likely used when animation is unnecessary such as the Pokédex.
4_22.bin is the animation sprite. it could be viewed as different parts that are later used for animating.
4_24.RECN is the cells file. I think this outlines each part of the sprite. im not really sure.
this is where it gets confusing and where it starts becoming unknown.
4_25.bin is an animation file. I think this file animates parts such as switching the image with a different image. im not sure.
4_26.RCMN and 4_27.RAMN are unknown and where we should be looking along with everything else.
I think one of them positions where each cell should be for the specified parts where as the other one rotates, stretchs, ect.
This is all speculation as to what they do
here is a documentation on the known file formats in the nds:
romhacking.net/documents/%5b469%5dnds_formats.htm#NCER
here is a thread on this specific page where it shows that RCMN and RAMN are indeed needed for animation
projectpokemon.org/home/forums/topic/13424-kazos-bw-tools/page/8/
edit:
I found a little mor information on RCMN and RAMN, it turns out that these are ds animation files, which is likely why there wasnt a lot of research done on these files.
problemkaputt.de/gbatek.htm#dsvideoobjs