Harold Pierre Hatecraft, shortened to H.P. Hatecraft, was one of Mystery Incorporated's closest allies and famous horror writers.
- 7: He complemented how weird music was these days.
- 8: He went as one of his creations to the Royal Knights Faire.
- 11: He went to a French restaurant for French people only, claiming his middle name was Pierre and he had French background.
- 12: He helped Mystery Incorporated solve the mystery of [[Char Gar
- 13: He wasn't allowed to enter the Cicada Bug Festival, but Mystery, Inc. invited him in as they were 'celebrities'.
- 14: In Scooby-Doo's dream, he was annoyed that he and his imaginary mystery solving friends didn't get kidnapped by Lord Infernicus, who burnt him in response]].
- 16: He was hypnotised by Aphrodite and danced with a rival author Regina Wentworth.
- 19: His books were seen on Vincent Van Ghoul's bookshelves.
- 20: At Destroido Corporation he hung out with Shaggy Rogers and Scooby. He visited the Oil Rig only once with the gang.
- 21: The gang saved him, a victim of the Manticore.
- 24: He went to Skipper Shelton's clam cabin, and Shaggy pushed him into the ocean.
- 25: He helped the gang solve the mystery of the Obliteratrix. His first name was revealed and he started dating Natasha Fenk.
- 26: He witnessed the unmasking of the Freak of Crystal Cove.
- 29: He was kidnapped by the Crybaby Clown.
- 31: He was invited to Brad Chiles and Judy Reeves' welcome home party.
- 32: He enjoyed the music at the art museum.
- 33: He watched the movie in the Crystal Cove Cemetery
- 36: When his girlfriend was kissing Don Fong, Daphne Blake said to Fred Chiles-Reeves she thought Fenk was dating H.P.
- 38: He went to Desdroido and witnessed the unmasking of the Scarebear.
- 41: He watched the play at the theatre and said to the gang they did a good job, and then witnessed the ghost of Gabriello Serra speak to the gang.
- 43: When the Skull Cattle attacked Crystal Cove, he said goodbye to the gang before getting crushed to death by the cattle, despite their efforts to save him.
- 52: In Post-nibiru, he was seen high-fiving Regina Wentworth.
- Episode 7
- Episode 8 (silent cameo)
- Episode 11
- Episode 12
- Episode 13
- Episode 14 (dream)
- Episode 16
- Episode 19 (mentioned)
- Episode 20
- Episode 21
- Episode 24
- Episode 25
- Episode 26
- Episode 29
- Episode 31
- Episode 32
- Episode 33
- Episode 36 (mentioned)
- Episode 38 (silent cameo)
- Episode 41
- Episode 43 (death)
- Episode 52 (Post-nibiru)
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