The show as a whole: “Two brothers follow their father’s footsteps as “hunters” fighting evil supernatural beings of many kinds including monsters, demons, and gods that roam the earth.” (from imdb)
The episode: At this point, the show had already established a meta-ish plot where there (for supernatural reasons) exists a pulp urban fantasy book series that exactly mirror the main characters lives. In this episode, they happen upon a con dedicated to the books, that also includes a larp.
It’s a fun episode, but it’s more on point about general geek culture than how larping is actually done (American con-larpers, feel free to correct me if I’m wrong).
Also: There are two newer episodes called “The Girl with the Dungeons and Dragons Tattoo” and “LARP and the Real Girl”, both guest starring Felicia Day, but I’m a few seasons behind and haven’t seen them yet.