Both shows are short crime comedies, so if you enjoy one you'll enjoy the other. Funny enough our leads in both shows are actually dating in real life (Kwangsoo and Lee Sunbin).

The Killer's Shopping List
+Short Run Time (8 episodes)
+Focuses on One Crime
+Very fun secondary cast

TeamBull Dog
+Excellent leads
+Case by Case Drama with buildup to a final case
+The entire team is great and have very unique roles
+Love the dynamic between characters

Second Season of Waikiki & The Sound of Your Heart Reboot, both fall under the "They Changed the Cast" umbrella. The only difference is Waikiki retains the funniest character for Season 2, but other than that both shows always draw comparisons to the original, but treating them as their own entities, makes them a lot more enjoyable. Both shows are sitcoms where the main cast ends up in wacky situations, and we get to watch how it plays out.

Yoon Shi Yoon, aka the master of double roles. In Train he plays 2 versions of the same detective with different personalities living in different worlds, while in Psychopath Diary, he plays the role of a timid office worker who believes he is a serial killer and has small bursts of moments where he "becomes" one.

Both shows also revolve around trying to find a serial killer. In Train the story focuses on finding who the killer is, while in Psychopath Diary the story reveals the killer in the first episode.

Psychopath Diary is more a comedic dark mystery, with moments that will make you laugh, while Train is more of a typical strict crime show. Both shows include crumbs of romance, but it is not the overarching focus.