Here is an idea I had for a chainsaw gag.

Take a chainsaw and cut a line into a wall in your maze.

Cut a piece of plywood that will cover the cut in the wall. Attach two springs to one end and attach the springs to the wall so that the plywood covers the cut in the wall.

Put some form of latch on the bottom of the "door" so that the plywood will lock when it clears the cut in the wall.

Some form of guide will be needed on each side of the "door" to keep it close to the wall and moving in a straight line. Guides could be used so that the cut could go at a 45 degree angle or horizontal.

The black line in figure 2 represents the cut in the wall

Remove chain from chainsaw blade first!

In this picture the victims are on the left side of the wall.

Place a bright light behind the door and actor so that when the door lowers light shines through the exposed cut.

I thought of adding an air line to the top of the chainsaw so air blows through the cut in the wall, just for that extra startle.

Start up the chainsaw and push down the door with the blade while pushing it through the existing cut in the wall. When the door is in the full lowered position it will get latched and stay "open" until released, springing back into closed position, waiting for the next victim.