Mysterious Origin.

Nobody really knows the true nature of the false hydra. Scholars the world over are left guessing as to the true nature of these creatures. What is known is that by the time their presence is apparent, it is often too late. The false hydra begins its life cycle as a lump of white flesh, growing and festering deep beneath the ground of a town or city. Their genesis is brought on by an abundance of lies and half-truths told by members of a community. Often these creatures manifest in kingdoms where propaganda has become out of control. Eventually, the small fleshy mass, no larger than a fist, grows to the size of a small child and sprouts a single head on a prehensile neck. This is when the false hydra truly begins its cycle. It burrows up through the ground until it reaches the surface, or a chamber with easy access to the surface of the ground such as a sewer, cave, or castle basement. Once it emerges, the false hydra begins to sing a deep and guttural dirge that can be faintly heard for miles around. This song makes all who hear it unable to perceive the false hydra. This is not invisibility, but something much more insidious. The false hydra removes itself from the mind of every sentient creature that can hear its song, meaning it can still be seen, but it is immediately forgotten by those who see it even as they stare directly at its moony face.  

Confabulation.

As the hydra begins to feed on the people of a town in order to grow larger and sprout more heads, locals are destined to notice something is amiss. They are going to wonder where the local priest has gone, or why their loved ones are no longer in town. The false hydra’s song will cause people to create new memories to make their new reality logical. those under the effects of the song might say things like “the baker isn’t just missing, he left town to fight in the king’s army”. These logical leaps become increasingly more difficult to justify as more people go missing. For example, someone who’s husband has been eaten by the false hydra might try to justify all the men’s clothing in their home by saying a visiting relative left them there. To an outsider, things will be obviously wrong, and to those trapped under the false hydra’s influence, the mounting weight of all this cognitive dissonance is liable to lead to madness.  

Horrid Growth.

The false hydra’s hunger knows no bounds. As the creature eats and grows both in size and number of heads, it becomes more bold. Once it has fully grown to a state of maturity it will drop all pretence and emerge from the ground as a mature false hydra. It then begins to sing a different song, one that dominates and enslaves the vast majority of those who hear it. The false hydra will have all who are able to resist its domination rounded up and eaten until it is sure that the remaining members of the population are enslaved to it. It will then have its thralls carry it on their backs to the next town, where it will continue to dominate and consume in a futile attempt to quench the unending appetite it holds. Eventually, the false hydra will become so large that it must be pulled by its thralls. It will have the creatures it is dominating wrap chains and rope around its body and drag the monster ever onward in a tour of blood and gore. Eventually, the false hydra will gorge itself into a non-sustainable position where it becomes impossible to eat enough to sustain its form. The least moments of a false hydra are usually spent gorging on its thralls in a final attempt to satisfy its appetite.  

Entropic Ends.

A false hydra will always inexorably eat itself to death. The only question is whether it takes days, weeks, months, or years. the best way to avoid a catastrophic result when a false hydra becomes a problem is to simply avoid it and remove its food supply. The ultimate safeguard, however, is prevention.  

Traits

Death Throes (Mythic Trait; Recharges after a Short or Long Rest).

When the false hydra is reduced to 0 hit points, it doesn’t die or fall unconscious immediately. Instead, it regains 214 hit points, then begins to wail and thrash about. It can no longer use its domination dirge. 24 hours after this trait becomes active, the false hydra dies.  

Legendary Resistance (3/Day).

If the false hydra fails a saving throw, it can choose to succeed instead.  

Multiple Heads.

The false hydra has seven heads. Whenever the false hydra takes a long rest, if it ate enough to gain proper sustenance during the day, it grows an additional head. While it has more than one head, the hydra has advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious.  

Neck Stalks.

The false hydra’s heads extend a long distance from its body. Whenever a head attacks a creature more than 15 ft. away from the body, the head provokes an attack of opportunity.  

Reactive Heads.

For each head the false hydra has beyond one, it gets an extra reaction that can be used only for opportunity attacks.  

Siege Monster.

The false hydra deals double damage to objects and structures.