SMBX2 can do everything 1.3 can, fixes some of its bugs, and adds more features than I can reasonably list here.
Yes, PNG files are default for all sprites in SMBX2. There's no need to use GIFs.
World map music, as implied in the last post, can also be changed. This is done by making a music folder in your episode folder and putting in a song of the same name as the song in basegame. File extension doesn't matter meaning you can replace an .ogg or .spc song with a .mp3 or .wav, too.
For more:
https://docs.google.com/document/d/1uOd ... vPFaA/edit#