This achievement can be a bit tricky and may require you to rotate the screen using the blue print located on the map and use
or
to rotate the camera accordingly.
The best level for this would probably be level 35 of the ‘Garden Party’ levels. Locate and pick up the dog and keep walking in the general direction of the ghost, wherever it may be and try to force it off screen. If the achievement does not unlock, try rotating the camera using the blueprint as mentioned and try to force the ghost off the bottom side of the screen. This may take a few attempts, but persistence will pay off here.