From Compendium of Worldly Lore
Bonded Summoners are mages that have an elemental companion and through exposure and growing closer with this companion they gradually become elementals themselves while progressing with their former spellcasting class.
Role: Spell Utility
Characteristics: Mage with elemental companion that gradually becomes an elemental as well
Source: Miniatures Handbook
Game Rule Information
The Bonded Summoner has the following game statistics.
Abilities: Whichever casting stat you used prior to prestiging, Intelligence for class skills, Constitution for bulk and Concentration
Alignment: Any
Hit Die: d4
Starting Gold: N/A
Class Skills
The Bonded Summoner's class skills are Concentration (Con), Craft (Int), Decipher Script (Int), Knowledge (all skills taken individually) (Int), Listen (Wis), Profession (Wis), Search (Int), Spellcraft (Int), 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 Bonded Summoner.
Weapon and Armor Proficiency: A Bonded Summoner is proficient with Bonded Summoners gain no proficiency with weapons or armor
Spells per Day: At every even numbered level gained in the bonded summoner class, the character gains new spells per day as if he had also gained a level in an arcane spellcasting class he belonged to before adding the prestige class. He does not, however, gain all the benefits a character of that class would have gained (metamagic or item creation feats, and so on), except for an increased effective level of spell-casting. If a character had more than one arcane spellcasting class before becoming a bonded summoner, he must decide to which class he adds the new level for purposes of determining spells per day.
Elemental Companion Ex: At 1st level, a bonded summoner picks his element of study: air, earth, fire, or water. This choice cannot be changed. The bonded summoner calls a Medium elemental of the type chosen, which replaces his familiar. The elemental gets abilities according to the information in the table below. At 3rd level, his elemental companion grows to Large. At 5th level, it grows to Huge. At 7th level, the companion becomes a greater elemental, and at 9th level it becomes an elder elemental. If the elemental companion dies, the bonded summoner takes damage equal to the elemental's Hit Dice. The bonded summoner also takes 1d4 points of damage to each ability score. A new elemental of the same kind as the old one maybe summoned 24 hours later. A bonded summoner may dismiss his elemental at any time without taking this damage, but he must still wait 24 hours before summoning another elemental.
Resistance to Energy Ex: A bonded summoner gains resistance 5 against the energy type associated with his element of study.
At 3rd level, this resistance improves to 10. At 5th level, it improves to 15. At 7th level, it improves to 20. At 9th level, the character gains immunity to the energy type in question.
Immunities Ex: Over time, a bonded summoner slowly turns into an elemental, gaining an elemental's immunities along the way.
At 3rd level, he becomes immune to sleep effects.
At 5th level, he becomes immune to poison.
At 7th level, he becomes immune to paralysis and stunning.
At 10th level, he is no longer subject to critical hits.
Cannot Be Flanked Ex: At 9th level, a bonded summoner has become so much like an elemental that he loses the normal human orientation toward "front" and "back." Like an elemental, he can't be flanked.
Elemental Form Su: At 10th level, a bonded summoner gains the ability to turn himself into an elemental and back again once per day. This elemental is an elder elemental of the bonded summoner's element of study. This ability functions like the polymorph spell, except as noted here. The effect lasts for 10 hours, or until the bonded summoner changes back. Changing form (to elemental or back) is a standard action that does not provoke an attack of opportunity.