fair points all. ....grave domain?
An NPC cleric doesn't need to have a full set of domain abilities, remember. We could just give it clerical Spellcasting. If it's Challenge 3, it's likely to be a decent spellcaster, maybe 6th level or so?
We could add on one or two Special Traits that feel appropriate for a Trog shaman if we feel like it, but it's not a necessity.
As for which domains to use as inspiration, isn't Grave more to do with necromancy than reptiles and caves? It doesn't seem terribly appropriate. Besides, is it SRD?