It would seem that you've not got a 'Ground' Tile on your Map. The Actor cannot move over non-existent Tiles, which is what the transparency is.
To have the Actor move around, you first need use a Ground Tile from the 'A' tab of the Tile-sheet. Grass, sand... Once there is a Ground to walk on, a Mountain, can be overlaid. By default, the two upper Tiles of the Mountain have Passage set to '*' (Star...), which allows Passage with the Actor displayed 'behind' the Mountain top.
Try making a Ground first, then add the Mountain, and the Actor will pass behind it.
Is this what you wanted..?