I assume you mean for the overworld. SMBX 2.0 works like this; anything seen from PGE, which is the editing side of the engine, loads INI files telling it how to show its graphics in it. When playtesting, or regular playing, the engine turns to TXT files telling it how to show the graphics ingame.
If you intend to add frames of animation to your scenes you need to make a TXT file with the following line:
N is the number of frames your image has.
Making an INI file also helps as it allows you to test how the image would animate without having to launch the game to see it in action.