To complete this, play as Lord Business in Free Play mode. The Relic Room can be found at the end of the 'Infiltrate Octan Tower' level. This level is located in Cloud Cuckoo Land (take the rocket ship to the right of the portal to a new area and slide down the slide. Access the level on the double-decker sofa).
Once in the Relic Room, you'll need Ma or Pa on the character wheel; if you position them between Lord Business and a targetable object (like the floor lights), you can hit the character when shooting the Kragle at the object. Then repeat with the other character to unlock the achievement!