Beautiful, very creative and well interpreted. it captures dipper and mable perfectly. the imps are well done and show some real originality. If I have any complaint it'd just be the lack of a background. But I digress, it's still a nice drawing. I peculiarly enjoy the facile expressions, I'm well aware that's easy thing to mess up. actually I'm kinda impressed just by the way his hand wraps around that bat, I always have a hard time getting hands to look right when I draw people. the coloring really good too, there are a lot of little touches on it that couldn't of been easy to put on, like the light shading on the cloths and the imps. all together great job, I hope to see a lot more art from you in the future.
That seems pretty much about right, with Dipper taking the direct approach while Mabel enjoys the moment. Sure enough she'll step up if things get too hairy (or bitey or kill-ly) but Dipper is okay at the moment.
Great job on the kids, and the little goblin ghoulies are kind of cute when they're not trying to murder/eat/enslave the kids. (Seriously, the dialogue is a tad violent for a children's show).