How many attacks of opportunity can a hydra make?

Question

The hydra gains as a bonus feat Combat Reflexes (Player's Handbook 92). However, the hydra description amends the feat to the following:

Feats: A hydra’s Combat Reflexes feat allows it to use all its heads for attacks of opportunity. (Monster Manual 156)

No further information is provided, and I'm at a loss. Here're the questions:

• Can a hydra make in a round only a number of attacks of opportunity equal to its number of heads? Equal to either the higher of its number of heads or 1 plus its Dexterity bonus? Equal to its number of heads plus 1 plus its Dexterity bonus? Something else?
• Does this natural ability grant a hydra special permission to bite a foe with up to all of its heads when a foe provokes a attack of opportunity? For example, Abe is in the threatened area of a 5-headed hydra. Abe foolishly retrieves an item from his belt pouch. This normally provokes one attack of opportunity from each creature that's threatening Abe. Can the 5-headed hydra instead make up to 5 attacks of opportunity—one for each of its heads—against Abe?

If it makes a difference—or makes answers easier to compose—, this specific 5-headed hydra has a Dexterity score of 20.

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Note: When I've used hydras in the past, they've been in their homes: in marshes where the PCs could evade them or stay out of their reach. The hydra for an upcoming encounter, on the other hand, is—I'm not making this up—in a 50-ft. by 50-ft. room. (Yes, Castle Amber is a very long adventure.) This hydra's inexplicably tiny lair means I can no longer avoid this baffling bit of rules text.

Answer 1

Googling suggests this issue has been both hotly debated and also no official clarification was ever given; the written text is ambiguous enough that many interpretations could be valid. However, I would personally rule that:

The hydra can make one attack of opportunity per round per head.

The normal purpose of Combat Reflexes is to allow a creature to make extra attacks of opportunity. It seems very unlikely to me that the amendment given in the Hydra's description is meant to convey that the hydra somehow makes special AoOs where it gets to use every head at once - that would just seem excessive. It seems rather more likely that this is simply about how many AoOs the hydra can make in a round (since that's what combat reflexes affects), and the hydra's version means it can make as many as it has heads, rather than the normal 1+Dex cap.

For the standard hydra this would be a notable improvement as it only has a dexterity modifier of +1, so gains several more AoOs out of this feat, and helps represent the independent nature of the heads. For the hypothetical high-dex hydra it's a less significant change. I'd be inclined to rule that the hydra gets to make as many AoOs as it has heads or 1+Dex, whichever is greater, in the event that its dexterity is higher than usual (and as it runs out of heads).

Answer 2

Answer by the rules as written:

• I) One action can only generate a single attack of opportunity.
• II) Combat Reflexes and Additional Attacks of Opportunity If you have the Combat Reflexes feat you can add your Dexterity modifier to the number of attacks of opportunity you can make in a round. This feat does not let you make more than one attack for a given opportunity, but if the same opponent provokes two attacks of opportunity from you, you could make two separate attacks of opportunity (since each one represents a different opportunity). Moving out of more than one square threatened by the same opponent in the same round doesn’t count as more than one opportunity for that opponent. All these attacks are at your full normal attack bonus.
• III) A hydra is allowed more attacks of opportunity in a roud due to special rullings on the Combat Reflexes feat that allows it to make more attacks of opportunity.

So for any given opportunity a Hydra would make only one AoO, but it can do this several times in a round as if its dexterity score was equal to the number of heads it has.

Answer 3

Disclaimer: The following is my own interpretation of the rules; since they are indeed less than clear.

A Hydra is a very special creature: it is composite.

The combat mechanics describe nearly autonomous heads and body. The heads have finite HP pools and can be targeted individually with specific attacks, while the body has a separate (though linked) HP pool and benefits from Fast Healing.

There are, at several points, emphasis on particular mechanics about the heads:

Hydras can attack with all their heads at no penalty, even if they move or charge during the round.

An opponent can strike at a hydra’s heads from any position in which he could strike at the hydra itself, because the hydra’s head writhe and whip about in combat.

Which to me seem to emphasize a few points:

• The Hydra's attacks are natural attacks; their numbers depend on the number of (presumably living) heads¹.
• The Hydra is attacking, not each head individually, single turn, single initiative roll.
• There is no need to track the position of each Hydra's head individually, as they are not separate creatures.
• Conversely, there is no safe side; killing the rightmost head does not make the right flank safe from attacks, any of the Hydra's head can attack any creature within reach of the Hydra.

In this context, my reading of:

Feats: A hydra’s Combat Reflexes feat allows it to use all its heads for attacks of opportunity.

would simply be a reminder that tracking the position of the heads is unnecessary, and therefore when the Hydra is in position to make an Attack of Opportunity, as long as it has at least a head, it can use it to perform the attack.

¹ This is also illustrated by the Attack and Full Attack actions in the table, where the number of bites is equal to the number of heads of the creature.

Answer 4

The two rules describe different amounts of time.

Combat Reflexes (emphasis mine):

Benefit: You may make a number of additional attacks of opportunity equal to your Dexterity bonus. With this feat, you may also make attacks of opportunity while flat-footed.

Normal: A character without this feat can make only one attack of opportunity per round and can’t make attacks of opportunity while flat-footed.

Thus your hydra can make 6 attacks of opportunity per round.

DMG:

Feats: A hydra’s Combat Reflexes feat allows it to use all its heads for attacks of opportunity.

this overides the general rule:

Combat Reflexes and Additional Attacks of Opportunity : ... This feat does not let you make more than one attack for a given opportunity...

thus combining the two:

Your hydra can make six attacks of opportunity per round and can make as many attacks per instance equal to it's number of heads.

For example:

Let's say your hydra has 3 heads left when Abe decides to run (provoking an attack of opportunity). Your hydra can then make three attacks (one for each head); leaving it with the ability to make three more attacks of opportunity during that round if another opportunity arises. Of course your hydra doesn't need to use all of it's heads if it decides to save an attack.

Answer 5

Your hydra may make up to five attacks up to six times.

Its no surprise hydra's Combat Reflexes feat rises questions - it is a unique form of special ability description. It seems, authors were trying to use as few words as possible not taking into account the fact the description like that is likely to cause issues. But there is some clue.

Hydras can attack with all their heads at no penalty, even if they move or charge during the round.

Bolded part indicates that hydra may attack with all of it's heads in place of an attack. Action taken in place of an attack may be taken during attack of opportunity as well as during a charge. So it is reasonable enough to assume hydra may attack with all of it's heads during every attack of opportunity. Text present is most likely just a reminder trying to say "don't forget, its all heads".

Is it a balanced and well designed ability? I think you can do better.

Hydras' special byte rules alone make it unique and notorious for their frequent appearance in different optimization treads. They are hardly broken, but they are definitely strong. So making that phrase in Combat Reflexes mean something less severe may be for the good. You may rule it only grants hydra a number of attacks of opportunity equal to the number of it's heads (but still only a single attack per opportunity). It would even make sense since all standard hydras have humble 12 as their dexterity scores.