Shortcuts in the Map Editor

Left Click
Places the currently selected tile

Right Click
Copies every tile on the clicked square and sets that combination as the currently selected tile

Shift + Left Click
Places the currently selected tile
BUT if the currently selected tile is an Auto Tile, then the base tile (without shadows or edges etc) will be placed instead
OR if Shift + Right Click was used prior to this click, places an exact copy of the currently selected tile

Shift + Right Click
Copies the selected tile exactly as it is and sets it as the currently selected tile (very useful when you don't want edges drawn on Auto Tiles)