Looks wonderfully gloomy and weathered, Spookilicious Mama. How are you planning to have it lit? I have one of these too, but our graveyard is relatively dark where I plan to use it so I was going to lighten parts of it to make it stand out more, so it won't get lost in the darkness. Similar to the more exaggerated painting done in the theater for darker scenes. I was going to try some combination of a dilluted white wash and a light dry brush with white to lighten the higher surfaces. But leave the recesses darker, like Rikki describes, for the contrast that makes it look less flat and gives it a weathered look.
But if your lighting is better or, especially, if you hit it with a spot light, then you probably won't have the issue I have. Check it out at night under lighting like you plan to use for Halloween and you can decide.
Are you going to have this be a tombstone, graveyard statuary, or something else?