Defining Polymorph's Text
The first point of confusion with the spell Polymorph is clarifying how exactly its text interacts with that of Alter Self. To that end, below is the combination of the two spells as if Polymorph was written as an independent spell instead of a derivative one. This was achieved by breaking both spells down line-by-line, then replacing lines from Alter Self with the respective lines from Polymorph, plus changing lines from Alter Self to refer to "subject/it" instead of "you/your" as-appropriate.
Polymorph begins with the line, "This spell functions like alter self, except that . . .." Typically, there are two separate ideologies for how to interpret this statement: "replaces" and "adds or replaces." For the former, it is assumed that any single element of Alter Self affected by a rule from Polymorph is completely stripped out and fully replaced by the new rules. For the latter, it is assumed that language from Polymorph is simply added to Alter Self unless an acute conflict is created, in which case only the conflicting language is removed from Alter Self.
This answer uses the "replaces" interpretation of Polymorph vs. Alter Self instead of the "adds or replaces" interpretation. The "adds or replaces" interpretation leads to strange rules that do not make much sense from the perspective of a player such as arbitrarily limiting a normally-Fine-sized creature, of which there are no standard player races, from becoming even smaller but otherwise not affecting size choices. So in all cases where a Polymorph rule relates to something directly ruled by Alter Self, the relevant Alter Self language has been discarded completely and replaced by the language found in Polymorph.
Level: Sor/Wiz 4
Components: V, S, M
Casting Time: 1 standard action
Target: Willing living creature touched
Duration: 1 min./level (D)
Saving Throw: None
Spell Resistance: No
You change the willing subject into another form of living creature. You can’t cause a subject to assume a form smaller than Fine, nor can you cause a subject to assume an incorporeal or gaseous form. The assumed form can’t have more Hit Dice than your caster level (or the subject’s HD, whichever is lower), to a maximum of 15 HD at 15th level. The new form may be of the same type as the subject or any of the following types: aberration, animal, dragon, fey, giant, humanoid, magical beast, monstrous humanoid, ooze, plant, or vermin.
Upon changing, the subject regains lost hit points as if it had rested for a night (though this healing does not restore temporary ability damage and provide other benefits of resting; and changing back does not heal the subject further). The subject gains the Strength, Dexterity, and Constitution scores of the new form but retains its own Intelligence, Wisdom, and Charisma scores. The subject's class and level, hit points, alignment, base attack bonus, and base save bonuses all remain the same.
The subject retains all supernatural and spell-like special attacks and qualities of its normal form, except for those requiring a body part that the new form does not have (such as a mouth for a breath weapon or eyes for a gaze attack). The subject keeps all extraordinary special attacks and qualities derived from class levels, but it loses any from its normal form that are not derived from class levels. It also gains all extraordinary special attacks possessed by the form but does not gain the extraordinary special qualities possessed by the new form or any supernatural or spell-like abilities.
If the new form is capable of speech, it can communicate normally. The subject retains any spellcasting ability it had in its original form, but the new form must be able to speak intelligibly (that is, speak a language) to use verbal components and must have limbs capable of fine manipulation to use somatic or material components.
The subject acquires the physical qualities of the new form while retaining its own mind. Physical qualities include natural size, mundane movement capabilities (such as burrowing, climbing, walking, swimming, and flight with wings, to a maximum speed of 120 feet for flying or 60 feet for nonflying movement), natural armor bonus, natural weapons (such as claws, bite, and so on), racial skill bonuses, racial bonus feats, and any gross physical qualities (presence or absence of wings, number of extremities, and so forth). A body with extra limbs does not allow the subject to make more attacks (or more advantageous two-weapon attacks) than normal.
The subject does not gain special qualities not noted above under physical qualities, such as darkvision, low-light vision, blindsense, blindsight, fast healing, regeneration, scent, and so forth. The subject does not gain any supernatural special attacks, special qualities, or spell-like abilities of the new form.
The subject’s creature type and subtype (if any) change to match the new form. The subject cannot take the form of any creature with a template, even if that template doesn’t change the creature type or subtype. Incorporeal or gaseous creatures are immune to being polymorphed, and a creature with the shapechanger subtype can revert to its natural form as a standard action.
You can freely designate the new form’s minor physical qualities (such as hair color, hair texture, and skin color) within the normal ranges for a creature of that kind. The new form’s significant physical qualities (such as height, weight, and gender) are also under your control, but they must fall within the norms for the new form’s kind. The subject is effectively disguised as an average member of the new form’s race. If you use this spell to create a disguise, you get a +10 bonus on your Disguise check.
When the change occurs, the subject's equipment, if any, either remains worn or held by the new form (if it is capable of wearing or holding the item), or melds into the new form and becomes nonfunctional. When the subject reverts to its true form, any objects previously melded into the new form reappear in the same location on its body they previously occupied and are once again functional. Any new items the subject wore in the assumed form and can’t wear in its normal form fall off and land at its feet; any that it could wear in either form or carry in a body part common to both forms at the time of reversion are still held in the same way.
Any part of the body or piece of equipment that is separated from the whole reverts to its true form. If slain, the subject reverts to its original form, though it remains dead.
Examining the Rules
With the spell defined more-clearly, we can now go section-by-section to determine exactly what Polymorph really does, arranged by paragraph:
Choosing a Legal Form:
You change the willing subject into . . .
- Size at least Fine
- Not gaseous or incorporeal
- Assumed form hit dice must be no more than the minimum of the caster level of the Polymorph spell or the subject's hit dice, to a maximum of 15
- The assumed form may be the subject's type, or any of: aberration, animal, dragon, fey, giant, humanoid, magical beast, monstrous humanoid, ooze, plant, or vermin
Effect on Subject Hit Points, Attributes, and Stats
Upon changing, the subject . . .
- Heals hit points as if resting for one night, but no other benefits from a night's rest
- Gains Strength, Dexterity, and Constitution scores of the new form
- Retains own Intelligence, Wisdom, and Charisma
- Retains own class, level, hit points, alignment, base attack bonus, and base save bonuses
- Note that the "hit points" in this statement contextually refer to the target form's hit dice rolled/average hit points absent any Constitution modifier. For example, a subject has d4 hit dice polymorphed into a magical beast type will not be able to re-roll its hit points to take advantage of that form's d10 hit dice, nor will its hit points be adjusted to match the average score for a creature of that type (the number listed in parenthesis). In other words, it is the hit points of the subject irrespective of its Constitution score. It is this DM's opinion that Polymorph does not change how the Constitution attribute functions. So while polymorph does not change the subject's hit points, it does change the subject's Constitution modifier. Changes to the subject's Constitution score can alter the subject's hit points even if the spell itself does not otherwise do so.
If a character’s Constitution score changes enough to alter his or her Constitution modifier, the character’s hit points also increase or decrease accordingly.
- There is an alternate interpretation of Polymorph's effect on hit points being that any possible change in Constitution simply does not count for hit point calculation; the presence of Polymorph should simply be ignored completely for the purposes of calculating hit points. This can be considered under the "specific > general" clause, but it is the opinion of this DM that such an interpretation is ignoring the context of how Polymorph handles the rest of its abilities and adjustments. No other effects of the Polymorph spell adjust fundamental game mechanics in such a way, but it is a possible interpretation.
The creature gains the physical ability scores (Str, Dex, Con) of its new form. It retains the mental ability scores (Int, Wis, Cha) of its original form. Apply any changed physical ability score modifiers in all appropriate areas with one exception: the creature retains the hit points of its original form despite any change to its Constitution.
Effect on Subject Special Abilities
The subject retains all . . .
- Keeps supernatural (SU) and spell-like (SLA) abilities unless the relevant ability requires a body part the subject does not have in the target form
- The subject keeps extraordinary (EX) abilities it earned from class levels
- The subject loses extraordinary (EX) abilities from its normal racial form
- The subject gains extraordinary (EX) special attacks from the target form
- The subject does not gain any SU or SLA abilities of the target form
- The subject does not gain extraordinary special qualities of the target form
Effect on Subject Speaking and Spell-Casting
If the new form is capable . . .
- If the target form is capable of speech, the subject may communicate normally
- This means the target form must be able to speak a language, not that it can simply vocalize some sounds
- The subject may still cast spells
- Spells with verbal (V) components require the subject to be able to speak
- Spells with somatic (S) components require the subject to have limbs capable of fine manipulation (gorilla fingers: yes, dog paws: no)
- Spells with material (M) components require that the spell components are still accessible / not absorbed into the form
Effect on Subject Physical Qualities
The subject acquires . . .
The subject does not . . .
- Keeps own mind
- Gains certain physical qualities of target form:
- Movement (max speed 120' flying, 60' otherwise)
- Natural Armor
- Natural Weapons
- Racial skill bonuses
- Racial bonus feats
- Gross physical qualities (i.e. shape and anatomy)
- Extra limbs do not grant extra attacks
- This refers to attacks from limbs, i.e. weapon attacks or attacks made with base-attack-bonus-based iterative attacks
- Natural Weapons are explicitly granted, but note that such attacks are not with the limb but a "claw" or "slam."
- For example: A human is turned into a girallon. The subject gains a bite and four claw natural attacks as well as a rend (EX) attack. The subject does not gain 2 more off-hand dagger attacks or attacks based on using the "limb" -- only the "claw" attacks are gained. If a girallon did not have a claw attack associated with its extra arms, then the subject would simply gain the gross physical quality of having 2 more arms, but would be otherwise unable to use those arms for attacking
- Another good example is the behir, which has six arm-like limbs, but those limbs can only be used as part of its Rake (EX) action and not with any other attack form.
- Does not gain any physical qualities not explicitly granted above, including (but not limited to) darkvision, low-light vision, blindsense, blindsight, fast healing, regeneration, scent, etc.
- The subject keeps their own non-EX physical qualities if they are not the ones explicitly gained from Polymorph. A quality in the above list that is EX would still be lost, since normal-form EX qualities are explicitly lost.
Effect on Subject's Type
The subject’s creature type . . .
- The type and subtype change to match the target form
- The "(if any)" clause on subtype simply means that a subject whose normal form does not have a subtype will gain one, and a subject whose normal form does have one will lose and/or change that subtype
- No templates allowed, no exceptions
- Incorporeal and gaseous creatures cannot be polymorphed
- If a creature's normal form has the shapechanger subtype can revert to their normal form as a standard action. This is an exception to the rule in which a creature's normal subtype changes to match the new form.
Effect on Subject's Appearance
You can freely designate . . .
- All appearance-related qualities are up to the discretion of the caster as long as the values are within the normal ranges for the target form
- Grants a +10 to the caster's disguise check
- This bonus probably also applies to the subject's disguise check if, for example, a rogue is the subject of another character's Polymorph spell, but then does its own disguise, but this is actually unclear
Effect on Subject's Equipment
When the change occurs . . .
Any part of the body . . .
- When a subject transforms to the target form, any equipment the target form is "capable of wearing or holding" is kept
- If an object is held in the hands, and the new hands can physically hold the object, it is kept
- Weapons can additionally make use of the sizing property (Magic Item Compendium, p.43) as a swift action to activate
- If an worn object will physically fit on the new form, it is kept
- Any equipment that is not "kept" is instead absorbed into the new form and made inactive for as long as the subject is polymorphed.
- When a subject resumes its original form:
- absorbed items reappear in their original locations
- any equipment held/worn that the original form can carry/hold are kept
- equipment the original form cannot wear/hold fall off and land at the subject's feet
- Polymorph on its own does not resize or reshape any equipment, so most mundane equipment that is not being held in the hands, assuming the target form has hands, will likely be absorbed if the target form is larger than the subject's current form. It will be DM discretion to what extent the subject can shrink and still physically be capable of wearing equipment, but it doesn't have to fit well, just fit at all.
- Any body parts or pieces of equipment separated from the whole revert to the original form
- A slain creature reverts to its original form and remains dead