My interpretation of whatever monster I feel like talking about, primarily from the 1st ed AD&D Monster Manual and Fiend Folio, but not limited to them, treated in a way that deals with the stuff I find interesting. That is: ecology and culture, if applicable. Stats can go hang.
Like an awful lot of the classical monsters and themes, the hydra has been relegated to the ‘boring’ category. The reasons for this are many and varied, stemming ultimately from each new generation of thinkers needing to reinterpret things and put their stamp on reality. When I read modern interpretations of the Hydra all I see is a big beast with multiple heads. However, this fails grasp the subtlety and the psychological complexity of the original monster.
The Hydra didn’t just have multiple heads. What it had was rapid regrowth of severed heads in response to attack. When a head was chopped off, two more grew in its place. Therefore, simply hacking off heads made things worse, not better. The way to deal with a Hydra was not to increase your aggression, because that only doubled your problem. Strike twice as fast? Find your foe grows at exactly the same pace. Your aggression only makes it stronger.
Now the funny meaning that occurs to me from this as a metaphor is the battle against terrorism. Terrorist fighters? Drone attack his family at a wedding. That’ll fix him! Well, no. All that does is make another crop of terrorists from the surviving kids keen to avenge the tragedy in their life.
But without delving too far into that, how can we use this as a tool to further a story in a role playing game? Clearly, simply running bare-arsed at a Hydra and chopping bits off is an invitation to failure. Any Fighter that thinks the answer to a Hydra is more hack-power deserves to die. No fighter should be allowed to hack off heads faster than they can regrow. This is specifically the message.
Hercules himself required aid in this task after getting his arse kicked in this simple first method. He employed someone to cauterise the wounds as he hacked the heads off.
What this tells us is that the fighter alone cannot defeat the Hydra. What he needs is help from other, sneakier compatriots. Slicing off heads is only part of the solution and can never succeed by itself.