We're big fans of useless machines around here: those boxes with one or more switches, that, when toggled, trigger some kind of arm that pops out and puts the switch back in the off position, before retreating to the inside of the box.
Greg Zumwalt's RIP Skeleton Instructable brings some much-needed Halloween boo-spookery to the genre, with a little, 3D printed electromechanical glowing-eyed skeleton who pops out of a coffin and turns the switch off before returning to its eternal rest.
The design is reminiscent of the electro-mechanical pinball machines I repaired for a local entertainment distributor while attending college some 40 years ago (we still have a fully functional electro-mechanical "Captain Fantastic" pinball machine, circa 1976, in our game room). Instead of a using a micro controller and servos, this electro-mechanical model uses a single motor and a two lobe camshaft to control the simple animation and lighting via two micro roller switches following the camshaft lobes. This approach greatly extends the battery life as when the model is idle, it draws no current from the twin AAA battery power supply. Note that RIP Skelton does not actually "press" the red button as his arm is too frail. He simply uses "mind over matter" (e.g. a roller switch on a cam lobe) to press the button.
RIP Skeleton [Greg Zumwalt/Instructables]