I'm currently making my SMB3 hack when I came across this issue, but it applies to any NES game.

I'm sure many of you are aware that many games use a 2x2 set of squares to create a single tile.  For example, the graphics of the Goomba enemy from the original Super Mario Brothers is made up of 4 squares, like this:



Well, my main problem is dealing with the tiles that you normally use for the world map in SMB3.  There are so many shared squares that changing a tile usually changes another.  I want to be able to change which of these graphic squares make up a tile so that I can modify things more freely.  Unfortunately, I have no idea how to do this.

Is there someone out there that knows how to do this?  If so, could you bring me through an example?

What you're referring to when you say 'which of these graphic squares make up a tile' is known as a tile map. Basically you have a whole bunch of tiles in memory and then there's a map that tells what tile should go where on the screen. If the utility InVerse pointed out to you doesn't do it, you'll have to do some reading on NES tile maps. I'm not familiar with the best NES documentation, but perhaps you can look at the SMB disassembly and look in the comments for tilemap references. Though that may be over your head at this point. Somebody else could probably recommend a better document to start with.

Thanks for the response guys.  I'll check out TSA and InVerse and mess with them for the next couple days. 

Kinda off topic, but anyway. Actually, the SMB gooba is four tiles. Theoretically it could have been three tiles, but it actually uses four. The reason for this has to do with some complicated stuff in the SMB sprite engine. (As part of the SMB Special hack I tried to get it to only use three tiles, I never did quite get it to work.)