The CLOUDS.DAT and DARK.DAT files contain the object sprite's frame information for Clouds and Darkside respectively.
The DAT files are 1452 bytes in size, with 12 bytes representing one object, for a total of 121 possible objects. Each block of 12 bytes is broken into three blocks of 4 bytes. The first block represents the first frame of the objects animation sequence. The second block indicates whether the sprite needs to be horizontally flipped or not. The last block is the last frame of the objects animation. Note, the first frame and last frame can be the same, indicating that the "animation" is just a static image. Most objects are static images. Each block of 4 bytes is broken into frames as front, left, back, right.
In theory, a modern system should be able to use dynamic memory to create more than 121 objects.