Horrible Assistants is a challenge in Ardorton Station that requires players to find the bodies of three dead lab assistants.
One assistant is behind Ardo Farm, in its southwest corner, next to a Dook Hut and a crate.
One assistant is in the higher level of The Psycho Surgery, in the middle of its south edge.
One assistant is a bit before the Infernal Machine. There's a small hallway, and two small rectangular rooms before it. In the top-left corner of the outer rectangle room, there's a small room with the assistant.