Even Bad Men Love Their Mamas: Lukesh dilligently cares for his mother, and when she calls him out on his suspicious behavior and claims she'll go to the FBI, he begins crying profusely as he kills her to keep her silent, then blames Reyes for making him do it.
Expendable Alternate Universe: Lukesh's M.O. With his ability to step between worlds, he commits horrible crimes in the one universe while living a normal life free of suspicion in the other. Ultimately the alternate Reyes and Doggett are both dead.
Punny Name: 4-D refers to the locker number belonging to Lukesh and also his ability to move through multiple worlds.
Reset Button: Reyes theorizes that Doggett accidentally moved between universes, displacing that universe's Doggett in the process. Doggett ultimately agrees and submits his own theory that the original Doggett will be able to return if he dies. Reyes takes Doggett off of life support and he dies, returning things back to normal, for our universe, at least.
Useless Security Camera: Although Reyes' place is fitted with all sorts of security cameras, Lukesh manages to warp into a blind spot and corner her. Fortunately, the prolonged absence of Reyes on camera is suspicious enough to bring everyone running just in time to save her.