A quick google will lead you to a host of Halloween-themed origami projects, but it can be difficult to find something suitable for folding with a class of students. This simple but effective origami bat by Nick Robinson (@nickorigami) is perfect. In addition, @senbazurueurope has made an instructional video (below), which may also be useful.
There are always lots of opportunities for mathematical discussion when folding origami with students. See my Origami in Lessons page if you are interested in learning more about using this wonderful art form in your classroom.
In addition Chris has provided a printable skull tile or 'tessera' for students to decorate individually and then combine to produce a whole-class (or school) tessellated Halloween display. This could look amazing!
There are other high quality tessellation resources on Chris' website www.tessellationart.com, including a beautiful short video explaining the concept of tessellations, and other tessellation templates for use in lessons. Definitely worth exploring.