Building a holy shotgun to eliminate local ghosts is quite the creative use of the limitation xD Not bad!
Here a little review:
The game itself is very simple. At first I thought it'd be a little boring, that the only task is to kill the same enemies over and over again. However, you pretty much saved that, since it's a short game and you could play the last section with a new weapon. Having a little less enemies and a simple switch puzzle within each area or something like that would have made the game feel more dynamic though.
Besides that, the only critique I have regarding the gameplay is, that the player moves a little too fast. Like that it's very difficult to aim accurately (and to not accidentally walk into enemies)
The games auditory aspect hasn't really been its strong point. The music loop became quite annoying very quickly.
On The visual side however I can say that the animations were very charming! Good job there.
I also liked the few dialogues, as they were written charmingly as well