Lemmings 2 data documentation in bitmap format.
An implementation to dump specified files as targa can be found at http://geoo.digibase.ca/lemmings/l2bitmap.cpp
Extracted .png images at http://geoo.digibase.ca/lemmings/l2bitmap.7z

Some of the files are compressed while others are not; as the compressed ones are easily identified by the character sequence 'GCSM', I won't note which ones are compressed and which ones are not.
All documentation refers to uncompressed data; so you'll have to use Mindless' lem2zip to decompress the compressed files.

The bitmap format is analogous to the bitmap format of the tiles in the style files, except that the size can vary.
The size of the bitmaps is not specified in the files themselves, and I haven't found a specification anywhere else either.
Therefore the descriptions will include the sizes of the individual bitmaps.
Same applies to the palette, so a sensible palette from a different file has to be chosen.
In this case the palettes have been taken from various .iff files, and for each bitmap I'll specify the .iff file and the palette ID.
To which data in the file this corresponds exactly is described in l2ss.txt.

The bitmap format is almost like a linear sequence of color entries, with the difference that first all pixels with
x-positions 4n are defined, followed by all pixels with x-positions 4n+1, then 4n+2 and 4n+3 (n is non-negative integer):

(x_size * y_size) bytes: list of colorIDs (from palette) for a certain pixel whose position is implicitely defined
	pseudocode description (by Mindless, adapted):

	p = 0
	for v = 0 to 3
		for y = 0 to (y_size - 1)
			for x = 0 to (x_size - 1) step 4
				pset((x + v, y), d[p]
				p += 1
			next
		next
	next
	
	(d is a byte pointer to the current tile, pset is a pixel setting function)

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Contents
----------------

font.dat
	palette: practice.iff (1)
	size: 102 bitmaps of 16x11
panel.dat
	palette: practice.iff (1), subtract 0x80 from each palette ID
	size:
		1 bitmap of 32x30, 
		1 bitmap of 32x20,
		59 bitmaps of 8x8,
		1 bitmap of 16x9,
		non-bitmap L2SS data (see l2ss.txt)
pointer.dat
	palette: practice.iff (1), subtract 0x80 from each palette ID
	size: 18 bitmaps of 16x16
rockwall.dat
	same as frontend/screens/rockwall.dat
vilscene.dat
	same as introdat/bckgrnds/vilscene.dat
frontend/screens/award.dat
	palette: award.iff (1)
	size: 320x200
frontend/screens/end1-5.dat
	palette: end.iff (1)
	size: 320x200
frontend/screens/map.dat
	palette: map.iff (1)
	size: 320x200
frontend/screens/menu.dat
	palette: menu.iff (1)
	size: 320x200
frontend/screens/rockwall.dat
	palette: practice.iff (1)
	size: 320x200
introdat/bckgrnds/black.dat
	a full one-colored (black) screen
	size: 320x200
introdat/bckgrnds/cosyroom.dat
	palette: waking.iff (2)
	size: 320x200
introdat/bckgrnds/nightvil.dat
	palette: intro.iff (2)
	size: 320x200
introdat/bckgrnds/vilscene.dat
	palette: talis2.iff (2)
	size: 320x200