Does this help? From the SRD...
Change Shape (Su): A creature with this special quality has the ability to assume the appearance of a specific creature or type of creature (usually a humanoid), but retains most of its own physical qualities. A true seeing spell or ability reveals the creature’s natural form. A creature using change shape reverts to its natural form when killed, but separated body parts retain their shape. A creature cannot use change shape to take the form of a creature with a template. Changing shape results in the following changes to the creature:
The creature retains the type and subtype of its original form. It gains the size of its new form.
The creature loses the natural weapons and movement modes of its original form, as well as any extraordinary special attacks of its original form not derived from class levels (such as the barbarian’s rage class feature).
The creature gains the natural weapons, movement modes, and extraordinary special attacks of its new form.
The creature retains all other special attacks and qualities of its original form, except for breath weapons and gaze attacks.
The creature retains the ability scores of its original form.
Except as described elsewhere, the creature retains all other game statistics of its original form, including (but not necessarily limited to) HD, hit points, skill ranks, feats, base attack bonus, and base save bonuses.
The creature retains any spellcasting ability it had in its original form, although it must be able to speak intelligibly to cast spells with verbal components and it must have humanlike hands to cast spells with somatic components.
The creature is effectively camouflaged as a creature of its new form, and gains a +10 bonus on Disguise checks if it uses this ability to create a disguise.
Any gear worn or carried by the creature that can’t be worn or carried in its new form instead falls to the ground in its space. If the creature changes size, any gear it wears or carries that can be worn or carried in its new form changes size to match the new size. (Nonhumanoid-shaped creatures can’t wear armor designed for humanoid-shaped creatures, and viceversa.) Gear returns to normal size if dropped.
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Alternate Form (Su): A creature with this special quality has the ability to assume one or more specific alternate forms. A true seeing spell or ability reveals the creature’s natural form. A creature using alternate form reverts to its natural form when killed, but separated body parts retain their shape. A creature cannot use alternate form to take the form of a creature with a template. Assuming an alternate form results in the following changes to the creature:
The creature retains the type and subtype of its original form. It gains the size of its new form. If the new form has the aquatic subtype, the creature gains that subtype as well.
The creature loses the natural weapons, natural armor, and movement modes of its original form, as well as any extraordinary special attacks of its original form not derived from class levels (such as the barbarian’s rage class feature).
The creature gains the natural weapons, natural armor, movement modes, and extraordinary special attacks of its new form.
The creature retains the special qualities of its original form. It does not gain any special qualities of its new form.
The creature retains the spell-like abilities and supernatural attacks of its old form (except for breath weapons and gaze attacks). It does not gain the spell-like abilities or supernatural attacks of its new form.
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.
Except as described elsewhere, the creature retains all other game statistics of its original form, including (but not necessarily limited to) HD, hit points, skill ranks, feats, base attack bonus, and base save bonuses.
The creature retains any spellcasting ability it had in its original form, although it must be able to speak intelligibly to cast spells with verbal components and it must have humanlike hands to cast spells with somatic components.
The creature is effectively camouflaged as a creature of its new form, and it gains a +10 bonus on Disguise checks if it uses this ability to create a disguise.
Any gear worn or carried by the creature that can’t be worn or carried in its new form instead falls to the ground in its space. If the creature changes size, any gear it wears or carries that can be worn or carried in its new form changes size to match the new size. (Nonhumanoid-shaped creatures can’t wear armor designed for humanoid-shaped creatures, and viceversa.) Gear returns to normal size if dropped.
