I know a pretty hack-ish trick to get things like mist in grasslands. It does, however, require you to have the Super ExGFX Bypass on for the current level. Basically, click
and disable the check box. Click OK and the whole level will screw up, however don't panic! Go to
and set the FG Graphics to the tileset that has the Layer 3 you're looking for (for mist, it's Ghost House). Click OK and go back to the Super ExGFX bypass dialog. Re-tick the check box and click OK. Then, click this:
. Set the Layer 3 to tileset specific and you're done!
Why this works is because the Super Graphics Bypass window only changes the graphics loaded and does not affect things like Tileset Specific Objects and Tileset Specific Layer 3.
Just note that if you're using tileset specific objects, they might screw up in some cases because as I said, you are going to change them.