The cake might be a lie, but these carvings are pretty legit. Whether you want to create the iconic Companion Cube or bring life to the misadventures of Stickman, these Portal stencils should do the trick.
But there are lots of other inter-spacial designs you can use to remind ghosts and errant trick-or-treaters to watch where they step, lest they fall through the very fabric of space. Give eager children false hope with a jack-o'-lantern that promises cake. Or check out this two-pumpkin teleporting Stickman design for a great front porch display that can be made even more Portal-tastic with orange and blue LED lights.