Radioactive Subject

Located in The Vatworks, Undermine. This rat can be found on the roof of one of the round, green tank-like buildings in the west of The Vatworks right above the entrance to Steamwheedle Laboratories, around 28, 71. Reaching it isn't trivial but one of the most reliable methods found so far is to obtain a Back-Strapped Missile and use it to reach the roof. These reusable rockets can be found occasionally in Undermine delves, in either the end chests or mislaid curiosities. Once you have one, you can stand at an optimal distance from the building, such as the ground around 32.2, 76.7 (there's often a Noggenfogger Recall Technician on a metal platform nearby), face directly at the building and launch. It may take a few tries to get it right.