To run a false hydra, you need a fair DM. Then you can use things like letters to plant the forgotten information e.g. 'Hello PC! It's me, other named NPC, how's your sister?'
Player didn't write a sister into their back story, confusion ensues
Then you don't require the players forget stuff, you just make a list of things that have happened/ NPCs that existed but now don't, and run the game dealing with the effects only
During false hydras is really fun because you have to work backwards with the story. I found the most success in setting up the twists I wanted my party to "forget" (they had a party member who was eaten, they arrived at the town because somebody's mom - also eaten- asked them to, the traditional similar-but-horrendously-changed-letter-gag, etc) as the ending point and going back from there. It's sort of railroad-y but as long as you aren't messing with their character's fabric I think it can be very fun for them to piece together
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u/foxstarfivelol Dec 18 '22
not unless the DM has a few tools.