To use URLs or upload pictures of custom sprites select the universe
none/custom and then
custom URL if you already have an URL you want to use or
upload sprite to upload a picture from your device.
If you want to use characters created using the
character creator or imported from the
community character list use the universes
owned characters or
imported characters at the bottom of the list.
It's recommended to create custom characters instead of uploading the sprites every time if you will use them often. You can also share them with friends and other users.
Sprites for the text box generator should be under the maximum size of 67*70px and be on a scale of 1:1 (every pixel is 1*1px).
If a sprite is bigger than that, the generator will resize it to the maximum size to make it fit. This will make it so it becomes blurry.
If you want your sprites to be recolorable only use black and white. Adding more colors will make it so only the pure white (or closest equivalent) changes.