The Knockout Nemesis 3000 is a weapon that is used by Chokun. It appears as a large sledgehammer with a black handle and a blocky gray head. According to its description, it is heavy enough to cause small tremors when used to strike the ground.
It's not so much a hammer as a block-shaped boulder. A little on the heavy side, but a safe choice both in battle, hitting something really hard to get people's attention, or creating minor tremors to scare off an enemy army.