Slime! It adds a certain "ickiness" to just about anything. If you need your set, mask, or prop to have permanent "goo", you might try Gorilla Max Strength Clear Construction Adhesive. It dries clear and shiny. Just load it into your caulk gun and go to town! This mask by Allen Hopps uses this glue for the drool: ...
Thought I'd work on sketching some of the things I see around me. Taking advantage of the stark angle of the sunlight. What did you do today? Happy Haunting!