This is the most well-known "S3E13" involving ghosts. It is a meta-episodic parody presented as a pilot for a reality TV show called Ghostfacers .
: During a Halloween train ride, a mysterious, cold little girl visits Hanna's mother, Ashley, at home. This girl is heavily implied to be a spirit, likely referencing the twin story Alison told in earlier seasons. Celebrity Ghost Stories (Season 3, Episode 13)
The story for varies significantly depending on which TV series you are referring to, as several shows have an episode with this exact designation or title. Supernatural (Season 3, Episode 13: " Ghostfacers ")
: Sam and Dean Winchester accidentally end up in the middle of a reality show investigation of the "haunted" Morton House.
: The amateur "Ghostfacers" team—Ed, Harry, Spruce, Maggy, and Corbett—gets trapped during a supernatural "lockdown". One of their members, Corbett, is killed by the ghost of a lonely survivalist named Freeman Daggett.
The series finale for the Netflix run of this sitcom used the title "Ghosts" metaphorically.
who was the little girl who came into hanna’s house? (s3 ep 13)