Tint the frosting green: in a mixing bowl, stir a few drops of leaf green gel food coloring into all of the white frosting until evenly colored.

Spoon the green frosting into a piping bag fitted with a 1A (large round) piping tip.

Pipe the outline of the Frankenstein face (a rounded square) onto your serving board.

Fill in the face by piping lines back and forth with even pressure, as if you're coloring inside the lines. Smooth the frosting with an offset spatula.

Scrape any remaining green frosting back into the bowl and stir in black gel food coloring until it turns black. Spoon about two-thirds of it into a second piping bag fitted with a 2D (large star) tip and pipe on the hair, holding the tip slightly above the board so it doesn't drag through the green frosting.

Twist apart 2 regular chocolate sandwich cookies and press the cream-side halves onto the face as the eyes. Press a mini sandwich cookie into the center of each for the pupils.

Spoon the remaining black frosting into a third piping bag (no tip needed) and snip a very small opening. Pipe on the mouth, a scar and stitches.

Arrange the cookies and pretzels around the frosting face and serve within 1 to 2 hours.