So now it's time to edit your OW in Overworld Editor. But how? Open the folder for Overworld Editor. You'll see a document that says "Sprites." Open that. Scroll down until you see this:
Code:
[BPRE]
Name = Pokémon Fire Red (English)
SpriteBank = &H3A3BB0
SpritePaletteHeaders = &H3A5158
SpriteCount = 153
To edit your sprite all you have to do is change the SpriteBank and SpriteCount.
the 3A3BB0 in SpriteBank becomes the location of your first new OW Offset.
First New OW Offset - 910000
The SpriteCount becomes the number of new sprites you've added. I've only added one, so mine will be changed to:
cHANGES ARE IN BOLD
Code:
[BPRE]
Name = Pokémon Fire Red (English)
SpriteBank = &H910000
SpritePaletteHeaders = &H3A5158
SpriteCount = 125
This can always be changed back if you need to edit the original OWs in the game, so don't worry about that right now.
Now open up Overworld Editor. What you should see is a bunch of black frames. Now you can draw or insert any OWs you want into them! Congratz! You can change the Palette here, so don't worry about doing that in Hex. And that's how you add a new OW to your game.
Step 2 - Adding the Sprite in A-Map
Spoiler:
The last step is to add your sprite in A-Map. This is a little tricky. First open A-Map and insert a sprite. The picture number is the number of the sprite in your New OW table. So since this would be the first sprite in our first new OW Table, it would be 00. If it were the 2nd sprite it would be 01 - the last sprite (256) - or converted to hex is FF - but the first new table can only hold up to EE, so it can only hold 240 sprites - the rest can all hold 256.
Okay, so for our first sprite we put 00 as the picture number.
Now we have to get the game to know we're using a different table. We do that by using the unknown variable directly below the picture number.
The sprite we're inserting is located in our first new table, but remember that the original table comes before this. So it's actually the second OW table in the game. So the first original table is 00, while the second table (the new table we inserted) is 01. So for the unknown data below this, we would write 00 01. If it were the ninth table we'd put 00 09 - the tenth table would be 00 0A.