If anyone of you is having trouble making your own theme, here's how.
Download the tool here (
https://gbatemp.net/threads/release-the ... ls.374206/)
Create a new BLANK BMP image with the dimensions 512 x 256 pixels for the top screen.
At the coordinates (0, 0) of that new image, insert the picture you want with the dimensions of 400 x 240. This will be the top screen.
Create a new BLANK BMP image with the dimensions 1024 x 256 pixels for the bottom screen.
Starting at coordinates (0, 0) of that new image, insert the three different images you want to transition on the bottom screen.
These three images should be each 320 x 240 pixels, and at coordinates (0, 0), (320, 0), and (640, 0) respectively.
Remember that these images will not fill up all of the white-space within the container BMP images. This is supposed to happen.
In the 3DS Theme Editor that you downloaded in step one, import the default theme by pressing File>Open and navigating to data/body_BZ.bin.
For slide 0, press File>Import and select the BMP Image you need for the top screen.
For slide 1, press File>Import and select the BMP Image you need for the bottom screen.
Once you're done importing, press simulator to do a test-run of your theme thus far.
If you're happy with your results, press File>Save to save your body_BZ.bin file.
