A very nice desert tileset made by supertailss. I've made some little edits and have added some new tiles.
Give credit to supertailss if used.
Your Map16 can be rearranged so that there are no blank tiles included when inserting it.
There doesn't seem to be any reason to make Map16 tiles 403, 404 and 405 act like ledges and the tiles below be passable when you already have 400 to 402 and below for that. Why not make the former tiles completely solid?
Those cacti could use more work to look like proper cacti, as their outline and surface are really smooth and spikeless as of now.
There are a couple of cutoff instances. Looking at the source material (MFGG submission), it seems that you got the normal slope tiles (Map16 tiles 42A and 42B) wrong, as the dirt's wavy decoration is supposed to be at the top of the tiles, not at the bottom. The steep slope tiles are completely missing it. Tile 1C0 in the ExGFX file is missing a couple of shading pixels to the left.