Toss together the Cheddar, Gouda, mozzarella and Monterey Jack in a medium bowl. Lay the white bread on a work surface and spread the pesto evenly on half the slices. Spread half the cheese mixture (about 1/4 cup per sandwich) on the bread with the pesto and top with the remaining white bread to make 4 sandwiches; place on a parchment-lined baking sheet.
Lay the dark bread on the work surface and spread the fig jam evenly on half the slices. Use the remaining cheese mixture and bread to make 4 sandwiches. Add the sandwiches to the baking sheet. Brush both sides of the white bread and dark bread sandwiches with melted butter. Bake for 5 minutes, then flip and bake for 3 minutes more.
Make the tombstones: Cut the crusts off the sides and curved tops of the white bread sandwiches, following the curves of the tops. Leave the bottom crusts on. Next, cut each sandwich in half lengthwise so that the pieces resembles tombstones.
Make the coffins: Cut the crusts off 3 sides of each sandwich, leaving 1 short side uncut. Halve each sandwich crosswise to make 2 long rectangles. Leaving a flat edge on the top and bottom of the short sides of each rectangle, make diagonal cuts at each corner to create a long hexagonal coffin shape. Add spooky decorations to the tombstones and coffins with the ketchup and mustard.
Spread the lettuce on a platter with a high lip. Lean the gravestones against the lip to stand up. Nestle the coffins in the lettuce.