sprite-composition.txt

Actual "game sprites" are composed of multiple "snes sprites" that are referred
to as "blocks" here.
The blocks are loaded from ROM on-demand, the composition data is transfered
from RAM to OAM on each vblank.

Each composition ("sprite info") block consists of
1 byte count of blocks
1 byte offset of blocks section
N bytes unknown (N = offset - 2)
count *
  1 byte flags
  1 byte X offset (signed)
  1 byte Y offset (signed)
  2 byte block index

block index points to 16x16 block list if lsbit is set in flags
and points to 8x8 block list if lsbit is not set in flags
see sprite-compression.txt for blocks

In the NTSC ROM the first "sprite info" appears to be at $ca0003, sprite infos
do not cross $xx8000 because of addressing mode. The last "sprite info" in a
bank will either end in a sprite with count=0 or end at an addres that can't
fit any more sprite infos before $xx8000 (addr&0xffff+2>=0x8000).
The next "sprite info" will then be at byte $0001 of the next bank:
  ie. $ca7fce -> $cb0001

It is unknown if data stored in $ca0000..$ca0002 and $xx0000 has a meaning,
but the game seems to use absolute addresses to "sprite info" structs, so
placement rules above are empirical.