Sonic 2 Hacking Guide
Binary - Mappings

Mapping objects refers to the process of taking several 8x8 sprites and putting them together to make a bigger sprite and/or object. This can be confusing, but it works quite effectively to give objects certain 'hot-spots'. For example, an enemy that touches the tip of Sonic's spines doesn't really bother him. However, if an enemy touches him elsewhere, Sonic gets hit and will either lose rings, lose shield, or die.

General

06FBE0 - Sonic mappings
07446C - Tails mappings

Ok, this is the section that tells where to read in the binary for mapping data for each of the 214 fames that Sonic has. Each set of 2 bytes identifies each frame in the order that they are put into the game. So, the first 2 bytes will tell where the mappings for the null frame are located. It works by starting at 06FBE0, and adding from that position to locate the data. Now that you understand this, you must understand the format of the actual mappings used. But first, you need to learn the header of each frame.

FORMAT:
#1 #2

1 - Number of sprite blocks for frame per 256
2 - Number of sprite blocks for frame per single

If the header has both bytes as "00", the object will be identified as a null frame. Remember that before the data starts for a frame, there is a 2 byte size header. Afterwards, the data begins. Now, you need to learn how to move, size, and other things with a sprite block.

FORMAT:
#1 #2 #3 #4 #5 #6 #7 #8

1 - Y position of sprite block
2 - Size of sprite block

The size works like this.

00 - 1 column, 1 row
01 - 1 column, 2 rows
02 - 1 column, 3 rows
03 - 1 column, 4 rows
04 - 2 columns, 1 row
05 - 2 columns, 2 rows
etc, etc, etc

It goes up to 0F (4 columns, 4 rows - 64x64). After this, the pattern repeats. Now to continue the mapping data.

FORMAT:
#1 #2 #3 #4 #5 #6 #7 #8

3 + 4 - 8x8 sprite selection
5 + 6 - ???
7 + 8 - X position of sprite block

Every sprite block has 8 bytes of data like this. Bytes 5 and 6 don't seem to have any apparent functions. Now you need to understand the 8x8 sprite loading selections. This allows you to give a frame sprites from another frame. By combining the mapping pointers and these, you can transform a frame into another one. Anyway, this is what you need to know.