I think I can help you out a bit.
Amduscias
Large Outsider (baatezu, evil, extraplanar, lawful)
Hit Dice: 26d8+208 (325 hp)
Initiative: +7
Speed: 30 ft
Armor Class: X (-1 size, +3 Dex, +X natural), touch X, flat- footed X
Base Attack/Grapple: +26/+40
Attack: Slam +35 melee (1d6+10)
Full Attack: 2 slams +35 melee (1d6+10) and bite +37 melee (1d8+5/19-20); or weapon1 +33 melee (dam) and weapon2 +28 melee (dam) and bite +31 melee (1d8+5/19-20) (don’t know if I got those values right)
Space/Reach: 10 ft/5 ft
Special Attacks: Bleeding wounds, constrict, fear, improved grab, rake, spell-like abilities, summon devils
Special Qualities: Alternate form, damage reduction 20/good and silver, darkvision 60 ft, regeneration 5, immunity to fire and poison, resistance to acid 10 and cold 10, see in darkness, SR 13+CR, telepathy 100 ft, tongues, unnatural aura
Saves: Fort +24, Ref +19, Will +23
Abilities: Str 30, Dex 17, Con 26, Int 24, Wis 25, Cha 37
Skills: Appraise +17, Bluff +42, Concentration +18, Diplomacy +50, Disguise +42 (+44 acting), Escape Artist +8, Gather Information +33, Hide +13, Intimidate +44, Jump +25, Knowledge (arcana) +36, Knowledge (history) +27, Knowledge (nobility and royalty) +31, Knowledge (religion) +36, Knowledge (the planes) +36, Listen +20, Move Silently +13, Perform (acting) +42, Search +17, Sense Motive +38, Spellcraft +19, Spot +20, Survival +7 (+9 other planes, +9 following tracks), Use Rope +3 (+5 bindings)
Feats: Combat Expertise, Dark Speech, Improved Critical (bite), Improved Initiative, Multiattack, Negotiator, Quicken Spell-Like Ability (fire shield), Two-Weapon Fighting, Vile Natural Attack (horn)
Environment: The Nine Hells of Baator
Organization: Solitary (plus X)
Challenge Rating: 21-23?
Treasure: X
Alignment: Lawful evil
Advancement: ---
Level Adjustment: ---
Alternate Form (Su): Amduscias can shift between his humanoid, unicorn, and wolf forms as a standard action. In humanoid form, he cannot ..., but he can use .... In unicorn form, he cannot ..., but he can use .... In wolf form he cannot ..., but he can use ....
Amduscias remains in one form until he chooses to assume a new one. A change in form cannot be dispelled, nor does Amduscias revert to any particular form when killed. A true seeing spell reveals all forms simultaneously.
Unicorn form:
Speed: 60 ft. (12 squares)
Attack: Horn +X melee (1d8+X vile plus bleeding wounds)
Full Attack: Horn +X melee (1d8+X vile plus bleeding wounds and 2 hooves +3 melee (1d6+X)
Abilities: Str 20, Dex 17, Con 21
Humanoid Form: Gains bite attack that deals X damage.
Fights with dagger (should have wounding to carry over from his unicorn form. It could even look like a unicorn horn) and short sword (unholy is always a safe bet. Dragonbane might be useful for keeping Tiamat's renegade servants and Bahamut's minions in line)
Wolf Form: Speed: 50 ft. (10 squares)
Gains Low-light vision, scent and a +4 racial bonus on Survival checks when tracking by scent.
Abilities: Str 25, Dex 15, Con 17
Bleeding Wounds (Ex): A wound from a Amduscias's gore attack continues to bleed after the injury was inflicted. Each wound bleeds for 1 point of damage per round thereafter. Multiple gore wounds result in cumulative bleeding loss (two wounds deal 2 points of damage per round, and so on). The bleeding can be stopped only by a successful DC 15 Heal check or the application of any cure spell or other healing spell (heal, mass heal, and so on).
Bolt (Ex): When in his unicorn form, Amduscias can Run as a move action.
Constrict (Ex): Amduscias deals XdX+X points of damage with a successful grapple check.
Fear (Su): As a swift action, Amduscias can frighten a creature within 30 feet. The affected creature must succeed on a DC 36 Will save or be frightened for 2d6 rounds. The save DC is Charisma-based.
Improved Grab (Ex): To use this ability, Amduscias must hit with his tail attack. He can then attempt to start a grapple as a free action without provoking attacks of opportunity. If he wins the grapple check, he establishes a hold and can constrict.
An opponent can attack Amduscias's tail with a sunder attempt as if it were a weapon. Amduscias's tail has X hit points. If Amduscias is currently grappling a target with the his tail, he usually uses another limb to make his attack of opportunity against the opponent making the sunder attempt. Severing Amduscias's tail deals X points of damage to him. If severed, Amduscias can reattach his tail instantly by holding it to the stump.
Rake (Ex): Wolf form only; attack bonus +X melee, damage XdX+X.
Regeneration (Ex): Good weapons, and spells and effects with the good descriptor, deal normal damage to ARCH. If ARCH loses a limb or body part, the lost portion regrows in 1d6 minutes. ARCH can reaattach the severed member instantly by holding it to the stump.
See in Darkness (Su): All baatezu can see perfectly in darkness of any kind, even that created by a deeper darkness spell.
Spell-Like Abilities: (Caster level Xth)
At will—charm monster (DC X), discern lies, dispel magic, faerie fire, fire shield (either version), greater teleport, locate object, produce flame, pyrotechnics, read magic, see invisibility, suggestion (DC X), telekinesis (5,000 g.p. maximum weight, DC X);
1/day—dominate monster (DC X), symbol of stunning (DC X).
Summon Baatezu (Sp): Once per day, Amudicias can automatically summon 1d6 abishai of any color or attempt to summon one aspect of Tiamat with a 20% chance of success. This ability is the equivalent of an 8th-level spell (CL 20th).
Tongues (Su): Amduscias can speak with any creature that has a language, as though using a tongues spell (caster level Xth). This ability is always active.
Unnatural Aura (Su): Animals, whether wild or domesticated, can sense the unnatural presence of Amduscias at a distance of 30 feet. They do not willingly approach nearer than that and panic if forced to do so; they remain panicked as long as they are within that range.
