The Priests is an extended version of the original short film. The director Jang Jae Hyun created the 12th Assistant Deacon and won many awards, so he then made a full movie with the same story line. Some of the scenes are exactly the same, but just done with different actors. I personally like the short film more, but the movie is pretty good too.
The plots aren't very similar, but the overall feeling of the two are the same. They both make you really creeped out and anxious as to what is going to happen next.
Exorcisms done by an experienced priest and a novice who has traumas and doesn’t know what he’s doing.
Both are Korean language short films that explore abusive superiors in the South Korean military. "12th Assistant Deacon" shows a short flashback to the abusive event and the long-lasting trauma it caused the victim while "Watch" is actually set on a military base.
These films have two totally different tones and themes, but they share the same depiction of sexual abuse in the South Korean military.