The thing I like about the unseen is each converted form is very similar to it’s previous class, with a few exceptions, one of those exceptions being priest.
Here is a way to keep the priest similar when converted:
The Monk
unseen support
Passive ability: Luck of the faithful
Immune to death once
Passive: Whispers of the grave
You can speak and listen to the dead at night as “priest”
Day ability: Bind soul
(1 use) your target will be immune to death tonight.
Night ability: Reanimate
(1 use) select an unseen player (possibly yourself), a class from a pop-up menu, and a dead player. If the target unseen member dies, they will appear to be the class you selected, and the dead player you selected will be revived. If they are a convert able class, they will become their unseen version.
Note: I do not know if this is balanced or not. I think it is?