The Sartarite Clan Generator has a question about the clan's ancient Chaos Foe. Most of the options are a group of things (Broos, Ogres, Scorpion Men, False Friends, Dragons. Even the Thing With Many Bodies is a group.) But there is also The Hydra, which seems to be a single specific thing. The only Hydra I've heard about is the Hydra of Hydra Hill in Dragon Pass, which is chaotic but doesn't seem to move around very much and which seems to be of army-level power and a single powerful thing, like Cacodemon or Cwim or so on). As a clan enemy it seems both extremely powerful (if it can fight an army, it can probably destroy a clan) and easy to avoid--just move away from where it lives. And yet it's continued to trouble the clan that has it as an enemy.
So as a recurrent Chaos Foe, it doesn't seem to work well. It's too big to easily fight, and yet this thing has to pose at least a periodic problem. The GM can't just decide that the Hydra is going to show up in the campaign this session because it's sort of like the Crimson Bat or Cwim just showing up one day--it's an existential threat.
How have people used this in their games?