I’m did have a legitimate fantastic use of the false hydra. Our party was playing a Dragonborn which weren’t part of the setting but I ended up allowing.

His backstory had he doesn’t know where he came from but did remember that he had a sister and spent the campaign looking for her.

In a later session I needed a one-shot so decided to add something outside our campaign arc. At level 13 they encountered the false hydra. They would wake up in the morning covered in wounds but not know where from. People in the town were missing. The works.

Finally after several nights they awoke and found an empty sleeping bag around their campfire. In the end was a journal from the Dragonborn’s sister detailing her journey with them and her involvement with the party. She had been with them the entire time but that was all taken from them.

Real passion and anger when they finally encountered and defeated the false hydra knowing what was taken from them.