So, I read a recent post about there not being a summon-based class ( base or prestige), and I agree, that could be interesting to have.
Hence my following suggestion of the Alienist (Complete Arcane variant, p. 21):
It will likely require some tweaking to make it work within the confines of Ravenloft, but I'll have a go at it:
(Original) requirements:
Alignment: any nonlawful
Skills: Knowledge (the planes) 8 ranks
Feats: Augment Summoning
Spells: Able to cast at least one summoning spell of 3rd level or higher.
Special: Must have made peaceful contact with an alienist or a pseudonatural creature.
(Tweaked) Requirements:
Alignment: any nonlawful
Skills: Lore 8 ranks
Feats: Augment Summoning
Spells: Able to cast 3rd arcane or divine spells
Special (possibly a good RP hook if an application becomes needed): Must have made peaceful contact with an alienist or a pseudonatural creature.
Hit die : d4
Skill points: 2 + Int
Class Features
Weapon and Armor Proficiency: Alienists gain no proficiency with any weapon or armor.
Spells per Day/Spells Known: At each level, an alienist gains new spells per day (and spells known, if applicable) as if she had also gained a level in a spellcasting class to which she belonged before adding the prestige class level. She does not, however, gain any other benefit a character of that class would have gained (improved chance of turning or destroying undead, a bonus feat, and so on). If she had more than one spellcasting class before becoming an alienist, she must decide to which class to add each level for the purpose of determining spells per day and spells known.
(Not sure if this can be implemented) Familiar Abilities : Levels of alienist stack with levels of any class that provide access to a familiar. Add levels from this class and the class that granted access to the familiar together and refer to the table on page 53 of the Player's Handbook to determine the familiar's natural armor, Intelligence, and special abilities. If a character had levels in multiple classes that grant access to a familiar before becoming an alienist, she must decide to which class to add each level for the purpose of determining the abilities of her familiar. This ability does not grant an alienist a familiar if she does not already have one.
(Original) Summon Alien: Whenever an alienist would use any summon monster spell to summon a celestial or fiendish creature, she instead summons a pseudonatural version of that creature. For example, by casting summon monster IV, she could summon a pseudonatural dire wolf. This adds the pseudonatural template (see page 160) to the summoned creature. An alienist gives up the ability to summon nonpseudonatural creatures with a summon monster spell. For instance, the alienist described above couldn't summon a mephit or howler with summon monster IV.
(Tweaked) Summon Alien : All summons become pseudonatural and gain the following benefits :
Acid & Electricity Resistance : 5 at lvl 1, 10 at level 5, 15 at level 10
Damage Reduction : 5/+2 at lvl 1, 10/+3 at lvl 5, 15/+4 at lvl 10
Spell Resistance : They gain spell resistance of 10 + Caster level
Alien Blessing (Ex): An alienist who attains 2nd level gains a +1 insight bonus on all saving throws, but she permanently loses 2 points of Wisdom.
Metamagic Secret: An alienist listens to the secret voices whispering from beyond time's end, and profits thereby. At 3rd and again at 7th level, she can choose any metamagic feat as a bonus feat.
(Original) Mad Certainty (Ex): At 4th level, an alienist's mad certainty in the power of entities beyond the reach of normal space and time lend her an unnatural fortitude, granting her an additional 3 hit points. However, constantly dwelling on such beings is mentally corrosive, and the alienist's mind begins to fracture. She now takes a —4 penalty on all Bluff, Diplomacy, and Handle Animal checks made to influence nonpseudonatural creatures.
(Tweaked) Mad Certainty (Ex): At 4th level, an alienist's mad certainty in the power of entities beyond the reach of normal space and time lend her an unnatural fortitude, increasing her hit die to d7. However, they take -4 penalties on Influence and Animal Empathy.
(Not sure if it can be implemented): Pseudonatural Familiar: Beginning at 5th level, an alienist's familiar, if any, gains the pseudonatural template (see page 160) in addition to the powers and abilities normal for a familiar of the appropriate level. This effect does not replace an existing familiar—the familiar has been slowly taking on pseudonatural aspects as the alienist rises in level, and those characteristics become fully functional at this point. From now on, the alienist's newly summoned familiars already possess the pseudonatural template. If an alienist has no familiar, this ability has no effect.
(Original) Extra Summoning: From 6th level on, an alienist gains one extra spell slot at her highest spell level. This slot can be used only for a summon monster spell. As an alienist becomes able to learn higher-level spells, the extra slot migrates up to the new highest level.
(Tweaked): Extra Summoning: From 6th level on, the alienist can cast Summon Creature 6 as a spell-like ability, once per rest. This improves to Summon Creature 7 at 7th level, Summon Creature 8 at 8th level and Summon creature 9 at 9th level.
(Original) Insane Certainty (Ex): At 8th level, an alienist's mad certainty crystallizes into a truly chilling mania. She gains an additional 3 hit points, but her mental faculties continue to degrade. Her penalty on Bluff, Diplomacy, and Handle Animal checks made to influence nonpseudonatural creatures increases to —10.
(Tweaked) Insane Certainty (Ex): At 8th level, an alienist's mad certainty crystallizes into a truly chilling mania. Their hit die changes to d10, and their penalties to Influence and Animal Empathy increase to -10.
(Original) Timeless Body (Ex): At 9th level, an alienist learns the secret of perpetual youth. She no longer takes ability penalties for aging and cannot be magically aged (see Table 6—5, page 109 of the Player's handbook). Ability score bonuses from aging still accrue, and any penalties the alienist might have already taken remain in place. An alienist is stolen away by horrible entities when her time is up, and she is never seen again.
(Alternative 1) Alien Knowledge : At 9th level, the alienist has learned much about the pseudonatural. Their summon spells lasts 1 turn/level, and they no longer have a chance to call up Dread Elementals
(Alternative 2) Eldritch Knowledge : At 9th level, the alienist's knowledge on the pseudonatural causes them to even warp the darkest of magical arts : If a dread elemental is called forth, it is bound to the alienist's distorted mind, much like a regular elemental summoning would be.
(Original) Alien Transcendence (Su): A 10th-level alienist, because of long association with alien entities and intense study of insane secrets, transcends her mortal form and becomes an alien creature. Her type changes to outsider. Additionally, she gains damage reduction 10/magic and resistance to acid 10 and electricity 10. Upon achieving alien transcendence, an alienist undergoes a minor physical change, usually growing a small tentacle or other strange feature, such as an extra appendage, organ, eye, or enigmatic lump. An alienist can hide this abnormality in a robe or hood, but the alien growth is not under the alienist's control and sometimes moves, twitches, opens, or otherwise animates of its own accord. This applies a —4 penalty on Disguise checks an alienist makes to conceal her true nature. Anyone who shares an alienist's predilection for study of the Far Realms immediately recognizes her transcendent nature, and she gains a +2 circumstance bonus on all Charisma- based skill checks and ability checks when interacting with such beings. She gains a +2 circumstance bonus on Intimidate checks involving any other creatures to whom she reveals her abnormal nature.
(Tweaked) Alien Transcendence (Su): A 10th-level alienist, because of long association with alien entities and intense study of insane secrets, transcends their mortal form and becomes an alien creature. Her type changes to outsider. Additionally, they gain damage reduction 15/+4 and 15 Electricity and Acid Resistance. Due to their eldritch nature, they gain a -8 on disguise checks.
Anyway, thoughts?