The Hydra Problem

 Discordian FifthDragon an image of this tumblr post the other day:

Interesting for sure, and with a very fine piece of art to go with it. But as people in the glog discord server riffed off this idea, suggesting their own variations, it made me think about the weird tension of hydras in adventure games. Like the troll and the vampire, the hydra's main gimmick is well-known. If you cut off a head, more will grow back in its place. Unlike the troll or the vampire, its gimmick is often quite avoidable if you endeavor to fight one. Rather than changing how you attack it, you ignore its special ability. Don't go out of your way to cut off a head-- just strike at the body as you would with any monster.

This isn't very fun. You want the monster to have the potential to do its coolest thing, but it would take an especially obliging player to willingly fall into the trap. Original D&D makes the regrowing of heads a special ability that only some hydras possess. Other rulesets might give the necks a lower AC or slow down the speed at which new heads grow to introduce some kind of risk-and-reward decision. Anytime I've run or played in a game which took such measures, they failed to encourage the heroes to consider trying to cut the hydra's heads. Most of the players I know are a little risk-averse, and often the mathematical considerations used to balance the dilemma are too obscure. Much safer, it was reasoned, to not engage with the hydra's special ability.

Some creativity can solve this. All you really need to do is give a proactive reason to slice at the hydra's heads. Here are some hydras for which the right circumstance can be set up without losing the element of risk inherent to the hydra's dilemma:

• Vampire hydra. You can try to use the standard vampire weaknesses, but it would be be hard to immobilize enough heads to drive a stake through its heart. Cutting each neck brings double smoke-particulate heads, but if you cut all the physical heads it is banished to its resting place to recuperate.
• Zombie hydra. Stupid, yet infectious. Cutting each neck brings double ghost heads, but if you cut off all physical heads you can send the fully-ghost hydra to its eternal rest by resolving its unfinished business. Usually this is embarrassing a demigod, fully killing a guy who's only mostly-dying of its poison bites, or telling its living descendants that it loves them and is proud of them.
• Lich hydra. A skilled, senile swordsman. Cutting each neck brings double mimic heads, then double rabbit heads, then double gorgoose heads, then double stirge heads, then its true death, which when destroyed ends the immortal fiend.
• Necromancer hydra. Intentionally kills the lesser heads to split off, then resurrects them. Rendering all original heads inert kills it.
• Skeleton hydra. If you cut off a heads, it doesn't double, instead snaking around as a necrophidius you may find more manageable.
• Pyrohydra. The classic fire-breathing hydra. Perhaps only the original heads can use its breath weapon?
• Philopater. The monstrous son of a vengeful god. You really don't want to kill this one, but severing a couple heads might give you enough opening to run away or hurry past it.
• Cosmic Hydra. Each head has a random alignment, and severing one might replace it with one or more allied heads.
• Mechanical Hydra. By summoning more pop-out heads, you create new weak points and even hiding spots in the torso of the monster.
• Cadmean Hydra. The hydra's blood is soldiers, gold, or some other desirable resource, and severing its heads is the most efficient way to access it.