INTROHi there!
I don't know how to exactly call this script, but I have looked in many places and found none. Plus, my internet is limited (currenly in Mozambique teaching computers).
The only script that does something similar is Pixelmovement1.6, but i think it can be made more simple.
So i came up with a new idea (as far as I know of): diagonal passability based on terrain ID.
I think it will work fine because it is simple. The way i tried to make it, i used 5 terrain IDs, one for each side of the prism and one to retain facing direction while in transition from tile to tile. (but my script wasn't working well, it was just some lines i added to some pixel movement script)
CONCEPTI made this pic to better explain the goals of that script, and I think that the picture is pretty much self-explanatory.

(X = non-passable; 1, 2, 5 and 0 are terrain IDs)
0 0 1 X X X 2 0
0 0 5 1 X 2 5 0
0 0 0 0 0 0 0 0
Another idea is to use only one terrain ID, and if front + side passable = false, then slide to opposite diagonal side.
Example:
0 0 1 X X X 1 0
0 0 1 1 X 1 1 0
0 0 0 0 0 0 0 0
WHAT SHOULD IT DO:If Terrain Id = 1 and hero walking from
left to right- change the sprite to a iso sprite
- lock facing direction (to make iso sprite match walking direction)
- move hero diagonally lower right in the same speed (either walking or running)
If Terrain Id = 1 and hero walking
up- change the sprite to a iso sprite
- lock facing direction (to make iso sprite match walking direction)
- move hero diagonally upper left in the same speed (either walking or running)
Should work for other directions too.
After leaving the corner or stop moving when facing a non-passable tile:
- stop moving
- change to normal sprite
- unlock facing direction
if there is any script for that out there: let me know.
else this is my request.
end
Peace
Cato