False Hydra thoughts - 01
As a monster stat block, a false hydra is not particularly compelling. Just give it a bonus action "You misremembered where you actually were" or something similar. Another fun thing to do is start them in combat, have them remove some HP, some spells, and make it clear that the PCs have been fighting for a little while. A terrible, terrible fight. But they don't remember it (or at least what happened up until this point). Combine them both for a suitably weird fight.
But false hydras are not about the fight. It's about the mystery. That's what makes them so compelling as a monster. They really ought to have 1 or 2 sessions dedicated to them.
I'll run through how I have run them successfully before, and we'll get to how we can condense this to a single encounter.
The biggest thing is that the False Hydra's existence is not the biggest mystery. Because we as people know what it is, it loses the compelling mystery of it.
A False Hydra is an inherently metagamey monster. Played as normal, the players are experiencing things their characters retroactively won't. Mix it up too much and it becomes a logistical nightmare. Do I remember what the disappeared person said? My character experienced this thing, didn't they?
And besides, once you know how they work, the magic is lost.
Best practice, I've found, is to shift focus. Remove the metagamey parts. Play it as if the characters are learning it at the same time as thr players. And most importantly, make sure the fact that there's a false hydra the less interesting or pressing mystery.
Instead, the mystery should be about the victims. Who were they? No one remembers! The best one to do is a party member. Give the party a quirky name, and leave clues behind that shows that they clearly loved the party, have been with them for a long time, and most importantly, feels like they could have been a fellow PC.
I tend to do it as a "You wake up in the tavern and there's an extra bed in your room with a note on it. It says "I figured it out. I'll be back soon. [Personal note to a PC, like 'When I get back, I have a great cookie recipe idea to try out'] [Initials]" and the party has no idea who this person is. (Side note, my favorite is a gnome wizard named Bartholomew Babblebrook)
The mystery becomes who this person was, what they were doing, do we trust that this was a real person, and how do we defeat what did this to them?
Keep clues to what this person was doing, like written records but no memory. Maybe they checked put a book, or had a painting commissioned.
And of course, some fun and thematic minor loot is great.
What about the song thing? That's important, right? Well, not really. The false hydra's method of removing memories doesn't need to be a song. Maybe it's sight. Maybe it's a scent. Maybe it's something in the drinking water. Make it so, even if the players catch on quick that it's a false hydra, there is still plenty to discover. Where is it hiding? Can we protect ourselves from its powers? How can we fight it?
Ok, how do we make all this happen in a single fight? Well, it'll take work, but I'm sure it'll be memorable.
We start with an in-media-res fight. Party has taken damage, and so has the foul beast. They don't know how they got here - the last minute or so is missing, but as they look up, they see an unfamiliar figure basically sacrificing themselves. They shout, "After this, we should have a chance!" They clearly refer to the party as friends, but there is no memory of them. They are then erased from existence.
As the party whittles down the false hydras health, or when the creature bites a party member, they can recieve memories of their fallen comrade. Maybe they make a save. On a success, they get the memories and on a fail, it's extra damage. Maybe it's automatic. Maybe they only get this info after the beast is defeated. You probably have a better idea of what's best for your table.
So that's my thoughts on false hydras lol
