1874 image of Fenrir, showing his monstrous size and imprisoned status.
This Fenrir is created by adding the Teratoid template (from the Immortals' Handbook) twice, then the Fiendish template, to a wolf (totalling CR 53). Finally I added "Divine Traits" as a hero-deity (a divine bonus of +3); according to Ascension this is worth +3 ECL, and thus +2 CR. He has taken the Divine Ability "Heavy-Handed" in exchange for 6 feats.
Fenrir CR 55
Chaotic evil Macro-Fine Magical Beast (Augmented Animal, Extraplanar)
Init +7, Senses Listen +54; Spot +54; darkvision 60 ft., low-light vision, scent
AC 127, touch -19, flat-footed 127 (-32 size, +146 natural, +3 divine)
hp 4000 (128d8+1792 HD); DR 30/-
Resist fire 30, cold 10; SR 56
Fort +103, Ref +86, Will +78
Spd 450 ft. (90 squares)
Melee Bite +131 melee (9d6+93/19-20)/ Claw +131/126/121/116 melee (9d10+93)
Base Atk +128; Grp +183
Space 360 ft.; Reach 240 ft.
Atk Options Power Attack, smite good, trip
Abilities Str 100 (+45), Dex 40 (+15), Con 70 (+30), Int 20 (+5), Wis 30 (+10), Cha 6 (-2)
SQ fast healing 50
Feats Cleave, Dire Charge, Damage Reduction (x10), Energy Resistance (fire x2), Fast Healing (x5), Great Cleave, Great Fortitude, Improved Critical (bite), Improved Initiative, Improved Spell Resistance (x14), Iron Will, Lightning Reflexes, Penetrate Damage Reduction (cold iron, silver), Perfect Health, Power Attack, Track (B), Weapon Focus (bite)
Skills Survival +4
Environment Any evil-aligned plane
Organization Solitary, pair, or pack (7-16)
Treasure None
Advancement --
The creature resembles a stocky, overmuscled wolf, but it is utterly immense, vast as a large hill. Its jaws drip foul-smelling black fluid; countless stained teeth as large as a man jut outward from its hideous mouth. Its fur is the color of spilled blood.
Fenrir (also called Hrothvitnir) is the son of the evil god Loki. He was born with monstrous form, gigantic size, and horrifying power - including a portion of divinity.
Fenrir is 160 feet high at the shoulders, 360 feet long (including a 80-foot tail), and weighs 12,800 tons.
Fenrir was once far more intelligent than he now is, but eons of imprisonment have made him totally insane. Now only a spark of mind remains, buried under irrational, destructive violence.
Fenrir is also the progenitor of the dreadful spawn of Fenrir, which plague many lands.
COMBAT
Fenrir has an enmity toward good outsiders and other obviously good beings, and will attack them in preference to other targets. Otherwise Fenrir fights like a wolf (though with much greater power) except that he will attack even if not hungry, since he is driven by madness caused by his long confinement.
Smite Good (Su): Once per day, Fenrir can make a normal melee attack to deal +20 damage against a good foe.
Trip (Ex): If Fenrir hits with a bite attack, he can attempt to trip the opponent (+59 check modifier) as a free action, without making a touch attack or provoking an attack of opportunity. If the attempt fails, the opponent cannot react to trip Fenrir.
Divine Traits: Fenrir is effectively a hero-deity and as such adds a +3 divine bonus to: armor class; attack rolls; checks (ability checks, caster level checks, skill checks, turning checks); difficulty class (for any special abilities, spell-like abilities, spells); initiative; saving throws and spell resistance.
Divine Abilities: Heavy-handed: Fenrir's strength bonus to damage is doubled.
Skills: Fenrir gains a +4 racial bonus on Survival checks made to track by scent.
IMPROVING FENRIR[]
Fenrir as described above has relatively few special abilities for a 128 HD creature. DMs may add any or all of the following additional special abilities if desired. They will probably increase Fenrir's Challenge Rating.
God-Eater (Su): Fenrir gains a bonus to his bite attack rolls equal to the divine rank of the target.
Impossible Jaws (Su): Fenrir, as the all-devourer, can swallow creatures which he could not possibly fit into his mouth, even those larger than himself. Whenever Fenrir scores a critical hit with his bite, he may make a grapple check as a free action without provoking an attack of opportunity. If the grapple check succeeds, Fenrir has swallowed the foe. Swallowed creatures take 8d6+31 bludgeoning damage and 31 acid damage each round. They can escape by making a successful grapple check against Fenrir or by dealing 100 points of damage to his interior (AC 83) with a light piercing or slashing weapon.
Regeneration (Ex): Fenrir has regeneration 60. Fire and holy weapons deal normal damage to Fenrir.
Soul-Shattering Howl (Su): Fenrir can emit this howl three times per day, filling a 640-foot cone with despair-inducing sound. All creatures in the cone must make a Will save (DC 72) or take 2d4 Charisma and Wisdom damage and be shaken for 4d6 rounds. The save DC is Charisma-based.
Stone-Smashing Howl (Su): Fenrir can emit this howl three times per day, filling a 640-foot cone with destructive sound. All creatures and unattended objects in the cone take 40d6 sonic damage (average 140); a Fortitude save (DC 72) halves the damage. The save DC is Charisma-based.
Summon Spawn of Fenrir (Sp): Three times per day, Fenrir can summon 1d4+1 spawn of Fenrir. This ability is the equivalent of an 11th-level spell.