From Compendium of Worldly Lore
Perhaps none of an arcane spellcaster’s mighty powers is so versatile, useful, or spectacular as the ability to change into something else entirely. The master transmogrifist is a sorcerer or wizard who has chosen to specialize in spells that change his form. The polymorph spell and other shapechanging transmutations offer the master transmogrifist the ability to become a fearsome juggernaut of physical battle, a swift flying traveler, or the perfect spy.
Since a character must achieve a significant level of competence as an arcane spellcaster to qualify for this prestige class, virtually all who choose this path are sorcerers or wizards. Of the two, sorcerers are more often drawn to the spontaneity and inventiveness offered by the polymorph spell and other spells like it.
Master transmogrifists delight in demonstrating their prowess with their favorite shapes and are thus sometimes amenable to putting on a show for powerful kings, wizards, or other transmogrifists.
Role: Spell DPS
Characteristics: Advanced polymorph users that have truly mastered their favored shapes.
Source: Complete Arcane
Game Rule Information
The Master Transmogrifist has the following game statistics.
Abilities: Whatever your casting stat is, your physical stats aren't super important as most of the time you'll be in your favored shape, probably Constitution as you do have a d4 hit die.
Alignment: Any Nonlawful
Hit Die: d4
Starting Gold: N/A
Class Skills
The Master Transmogrifist's class skills are Bluff (Cha), Concentration (Con), Craft (Int), Disguise (Cha), Knowledge (arcana) (Int), Listen (Wis) Profession (Wis), Search (Int), Spellcraft (Int), and Spot (Wis).
Skill Points at 1st Level: (2 + Int modifier) × 4
Skill Points at Each Additional Level: 2 + Int modifier
Class Features
All of the following are class features of the Master Transmogrifist.
Weapon and Armor Proficiency: A Master Transmogrifist is proficient with whatever they were already proficient with prior to taking levels in this class.
Spells per Day/Spells Known: At each level indicated on Table 1-1, a master transmogrifist gains new spells per day (and spells known, if applicable) as if he had also gained a level in an arcane spellcasting class to which he belonged before adding the prestige class level. He does not, however, gain any other benefit a character of that class would have gained (such as the bonus feat sometimes gained by a wizard). If he had more than one arcane spellcasting class before becoming a master transmogrifist, he must decide to which class to add each level for the purpose of determining spells per day and spells known.
Extended Change Ex: A master transmogrifist gains the benefit of the Extend Spell feat on any transmutation spell he casts to change into one of his favored shapes (see below). This benefit does not increase the spell's level or casting time or require any special preparation. Spells that can benefit from this ability include alter self, polymorph, polymorph any object, and shapechange.
Favored Shape Su: A master transmogrifist chooses three favored shapes at 1st level. A favored shape is a specific kind of creature whose form he can assume by means of the polymorph spell. He cannot choose a creature of his own type (humanoid, most likely) as a favored shape. For example, an 8th-level human sorcerer/1st-level master transmogrifist might choose pegasus, umber hulk, and bronze dragon as his favored shapes, though because of the Hit Dice restriction, he could become only a very young bronze dragon. A master transmogrifist gains a number of advantages with his favored shapes, as noted in the following class feature descriptions. At every odd-numbered level beyond 1st, a master transmogrifist gains one additional favored shape. Thus, he has four at 3rd level, five at 5th level, six at 7th level, and seven at 9th level. Furthermore, once per master transmogrifist level beyond 1st, a character can choose to lose a previously chosen favored shape and select a replacement.
Manifest Senses Su: At 2nd level and higher, a master transmogrifist gains the senses of his favored shape when he assumes its form. Senses include extraordinary special qualities such as blindsense, blindsight, darkvision, low-light vision, scent, and tremorsense.
Battle Mastery Ex: At 3rd level, a master transmogrifist gains a +2 competence bonus on all attack rolls he makes while in one of his favored shapes. This bonus increases to +4 at 6th level and to +6 at 9th level.
Effortless Change Ex: At 4th level, a master transmogrifist learns how to change his form through a simple act of will. He can choose to apply the benefits of the Still Spell and Silent Spell feats (even if he doesn't have the feats) to any transmutation spell he casts to change into one of his favored shapes. This benefit does not increase the spell's level or casting time or require any special preparation. Spells that can benefit from this ability include alter self, polymorph, polymorph any object, and shapechange.
Shapechanger Ex: A master transmogrifist acquires the shapechanger subtype at 5th level. He also gains the ability to remain in an assumed form indefinitely when he casts alter self. This works exactly like the Alter Self spell except that the duration is permanent. In other words, a master transmogrifist can remain in the form he assumes as long as he wishes, until either he chooses to dismiss it or the alter self effect is dispelled.
Reflexive Change Ex: At 7th level and higher, a master transmogrifist has the ability to change into a favored shape via a transmutation spell in response to an opponent's action once per day. If he has an appropriate spell prepared and chooses to use this ability, he can change form as an immediate action in response to the action of another creature. For example, a master transmogrifist might turn into a dragon turtle to gain a high Armor Class against an impending attack or change into a red dragon to gain immunity to the fire damage of an enemy's fire storm spell. The spell is expended as if the transmogrifist had cast it normally, and he remains in his new form until either the spell's duration expires or he dismisses it. A transmogrifist gives up his next action to make a reflexive change. If a master transmogrifist is currently under the effect of a shapechange spell he cast on himself, he can use his reflexive change ability as often as he likes (although never more than once per round). Each time he uses it, he loses his next action.
Manifest Qualities Ex: At 8th level and higher, a master transmogrifist has all the extraordinary special qualities of any favored shape he assumes. For example, he could change into a troll to make use of the troll's regeneration ability, or take the form of a green hag to gain spell resistance 18.
Infinite Variety Su: At 10th level, a master transmogrifist gains the ability to create completely imaginary forms when he casts polymorph, polymorph any object, or shapechange on himself. To create an imaginary form, he chooses one of his favored shapes as a base form. He can then choose a single aspect of a second monster whose form he could assume using the spell he is casting and add it to the first creature. His available options include the following.
Replace the base form's natural armor bonus with that of the second form. Add the second form's movement modes. Add one of the second form's natural attack types (with the appropriate reach), if the base form doesn't have that attack type already. Add an extraordinary special attack of the second form. Add an extraordinary special quality of the second form. Replace one of the base form's physical ability scores, if both the base form and the second form are the same size category.
For example, if a young red dragon is the base form and a giant octopus is the second, a master transmogrifist could add the octopus's eight tentacle rakes (damage 1d4 + Str bonus) to the dragon's available natural attacks.