This giant spider appears above Midway Pier.
Assembling the effigy is straightforward. There is a base, a center piece with flat metal bottom that goes into it, legs on each side, and a spring on its butt. The sides go together non-symmetrically. There's a gear connection further forward on one side and further back on the other side. The pieces might float above your head, so remember to look up if you're missing a piece.
Once activated, this guardian is the Midway Pier metalwork above the fair. It creaks to life, and the head glows with 5 large dots. The center dot will light up a laser sight and then produce a powerful beam shot once its aim settles on a pillar. It's confusing to see exactly where the spider is moving, due to the complexity of metal beam structures and night-time lighting, but the laser sight is fairly bright and broad. When it starts, it targets pedestals randomly. Once you attack it, it will spin around and shoot the pedestal you're on - move! You won't have much time to dodge. Shoot and move, shoot and move.
To attack the spider, aim for the glowing eyes.