A 12V battery can kill you or seriously harm you. The entire chassis of the vehicle is the return path, and can make a short circuit or exposed wire exceptionally dangerous. Working around high current paths like the wire from the alternator can be a special hazard.

The battery can also release explosive gasses if charged or used improperly or if other parts of the electrical system are damaged. Combined with a spark and again death and serious injury are possible.

Pulleys and belts are under tension. It's probably not as lethal, but it's a stored energy hazard and has hurt plenty of technicians.

Suspension systems contain many stored energy hazards.

Tires with air pressure are a stored energy hazard, even if they're not attached to the vehicle.