casting at a hydra

[Aeson]

If you cast a spell on a hydra should the DM roll saves for each head?

 

[Beckett]

No. Magic effects only affect the creature's body (although area effect spells can seal off the necks if they do fire or acid damage).

 

[frankthedm]

A hydra can be killed either by severing all its heads or by slaying its body. To sever a head, an opponent must make a successful sunder attempt with a slashing weapon. (The player should declare where the attack is aimed before making the attack roll.) Making a sunder attempt provokes an attack of opportunity unless the foe has the Improved Sunder feat. 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. An opponent can ready an action to attempt to sunder a hydra’s head when the creature bites at him. Each of a hydra’s heads has hit points equal to the creature’s full normal hit point total, divided by its original number of heads. Losing a head deals damage to the body equal to half the head’s full normal hit points. A natural reflex seals the neck shut to prevent further blood loss. A hydra can no longer attack with a severed head but takes no other penalties.

Each time a head is severed, two new heads spring from the stump in 1d4 rounds. A hydra can never have more than twice its original number of heads at any one time, and any extra heads it gains beyond its original number wither and die within a day. To prevent a severed head from growing back into two heads, at least 5 points of fire or acid damage must be dealt to the stump (a touch attack to hit) before the new heads appear. A flaming weapon (or similar effect) deals its energy damage to the stump in the same blow in which a head is severed. Fire or acid damage from an area effect may burn multiple stumps in addition to dealing damage to the hydra’s body. A hydra does not die from losing its heads until all its heads have been cut off and the stumps seared by fire or acid.

A hydra’s body can be slain just like any other creature’s, but hydras possess fast healing (see below) and are difficult to defeat in this fashion. Any attack that is not (or cannot be) an attempt to sunder a head affects the body.

Targeted magical effects cannot sever a hydra’s heads (and thus must be directed at the body) unless they deal slashing damage and could be used to make sunder attempts.

 

[Hypersmurf]

I suspect the original question is not in relation to damaging spells, but rather Enchantments and the like.

Do you Dominate a hydra all at once, or one head at a time? Is the hydra's body subject to mind-affecting spells?

Sean K Reynolds took this into account with his Two-Headed Mutant template:
Dual Mind (Ex): The mutant has two brains, so for all mind-affecting attacks the mutant counts as two separate creatures. If a spell or effect can only affect one of the creature's heads (such as a charm monster spell, which affects a single target), the unaffected head takes control of the entire body. In these situations, the affected head becomes inert for combat purposes (losing its extra bite attack, if any), and the creature temporarily loses its Dual Reflexes ability. Even if one head is charmed or dominated, the creature does not attack itself or split its attacks between its normal opponents and those chosen by its controller. In effect, mind-affecting attacks must affect both heads in order to achieve the normal result (casting two successful charm monster spells on a two-headed mutant brings it fully under the control of the caster and allows it to use all of its abilities).

Interestingly, neither the Multi-Headed template in Savage Species, the Ettin, nor the Hydra give this any thought.

For the hydra, Frank's highlight is relevant, though unsatisfactory:
Targeted magical effects cannot sever a hydra’s heads (and thus must be directed at the body) unless they deal slashing damage and could be used to make sunder attempts.

So Dominate Monster cannot be cast on the heads; as a targeted spell, it must be cast on the body, and will take effect normally... despite being a mind-affecting spell targeted specifically on a part of the creature that isn't its head...

-Hyp.

 

[Slaved]

So Dominate Monster cannot be cast on the heads; as a targeted spell, it must be cast on the body, and will take effect normally... despite being a mind-affecting spell targeted specifically on a part of the creature that isn't its head...

Perhaps it thinks more with its stomach anyway.

 

[Len]

So Dominate Monster cannot be cast on the heads; as a targeted spell, it must be cast on the body, and will take effect normally... despite being a mind-affecting spell targeted specifically on a part of the creature that isn't its head...

Makes sense to me. Who says the hydra's brain is in one of its heads?

 

[Corsair]

Makes sense to me. Who says the hydra's brain is in one of its heads?

Also makes sense, because lopping its heads off would make it stupider otherwise. Which clearly doesn't occur.

 

[MarkB]

Makes sense to me. Who says the hydra's brain is in one of its heads?

Yes, I've never really thought of hydras as being multi-brained, but assumed they kept their brain back in the body somewhere and used the heads purely for attacking, eating, breathing and senses. That may well have been a subconscious result of having read about Niven's puppeteers.

 

[moritheil]

So a daggerspell mage could try to modify a spell to sever a head, but black blade of disaster could not be used to sever a head?

 

[Aeson]

I can't remember the spell right now but the players argued that I should have rolled a save for each head rather than once for the creature as a whole.

I think they feel if the heads can attack different targets that they should each make a save versus the spell.