Do you mean like running over a custom power up causing a grav lift to destroy something to like get ride of the floor or a simple couple of pallets that you can fall throgh?
I would like to link you to this thread. on how to make a trap door. Also, this thread can help you find what you need when you are Forging. I hope this helped and feel free to ask me any questions you may have in the future. All of the best, COMMANDERMATT1