Maximum CR - The Titans of the Shadow Realm, the Avi'yark

Avi’yark
The Avi’yark are the titans of the Shadow Realm. It is a beast of 6 legs, and any one of them can be used as a hand with powerful claws. It has a long neck with a head that closely resembles a lion’s with 6 eyes. It has a thick mane that runs from its head and down along its spine to the tip of its long, powerful tail. Thick wooly fur covers its entire body, with an unknown array of colors and patterns
Timeless, eternal, immortal, the Avi’yark hate the Shadow Realm, and will attempt trickery, hypnotism, false friendliness, or even seduction to get out. The shadow realm has turned their once lovely coat into an inky blackness, and their lovely eye gems have become nothing but a white glow, and so they will stop at nothing to acquire a shadow mana object, the only known key to unlocking their wretched cell and endless torment.
Summoner beware; these gargantuan beasts will do anything to get what they want – and your summoning contract won’t save you forever. It is highly un-recommended to summon an avi’yark from the 35th circle of magic. One such creature anchored itself to its summoner and eliminated half of a world’s population on its quest for vengeance and freedom before three deities intervened to send it back to its realm.
It is not recommended that one ever summon an avi’yark.
Semi-Magical Beast – CR: 12000 Size: 100’x80’
HP: 1,600,000,000 WP: 800,000,000
MP: 200,150,000 SP: 100,075,000
Init: Multi-Phase 14: +764 (+11) Hit: +28000 (+437)
Dodge: +12000 (+187) Block: +34000 (+531)
Def: 40000/40000(80000) M.Def: 34000/34000(68000)

I thought I'd just interject a moment and mention that deities in TwV have a CR between 500 (for lesser,) and 3000 (for greater.) The avi'yark makes the very deities cringe at its power.

Quite Boring, Really: If summoned into the normal realm, it won’t do anything unless the summoner shows a willingness to help it in escaping the shadow realm. Otherwise, they’ll merely stand and give commentary on how boring everything is, even in the midst of a furious combat. The only time it’ll attack is if someone deals more than 1,000 points of damage in a single hit, (because that’s about where they feel it,) at which point they will promptly step on the annoyance. This trait is negated against deities, as they will go into a rage against deities, looking to steal power to fuel their escape! When they are talked into fighting, they have no regard for the safety of their summoner, (whether they agreed to help them or not,) and will freely use AoEs with reckless abandon.
Taunting: Unless directly ordered to kill an enemy, they would much rather taunt them. Lifting them daintily and looking creatures over as they flail helplessly is a form of amusement. They will taunt beings about their short lives, and their flaunting ways, and how one day they shall unlock the shadow realm, and woe comes unto the world as they will obliterate every last one of the puny creatures on the normal realm.
Fly Swat: Power-swiping down onto an opponent that has less than 100 current CR (like a warehouse falling on your head,) will cause instant death. They will look completely un-amused at the act. This is often their first reaction when a summoner goes through all the talking of helping them out… and then just asks them to kill one person. The same can go for just smashing one building. What a bore.
Arcane Breath of the Ancients: Much like dragon breath, an avi’yark can expel a deathly energy from its mouth. The breath initially hits a fan of 20’, and deals 3d6*5 neutral magic damage. For every 5 MP, or 1 SP used on this ability, it gains 5’, and raises the multiplier to the damage by 1. For 6000 MP, it can add +Magic onto the end of the damage, (after the multiplier.)
Host for My Anchorage: If summoned at 100% power, an avi’yark will use this ability first. It binds their soul to the soul of the caster, making them able to stay in the normal realm without the caster’s upkeep. This is usually when they bite off the caster’s limbs to prevent dispelling, and then string them around their neck like a charm as they hunt down shadow mana objects.
Aura of Absolute Power: All allies, opponents, and non-participants within a mile of this creature have the bonuses adding to their initiative rolls, offensive rolls, and defensive rolls all divided by 64, (including this creature.)
Bite: When making a bite attack against a big target, they deal 1d20*12000+400000 Crushing Damage. They can take this action up to 16 times in a turn, if they wish.
Devour: When attacking a smaller creature, the avi’yark can simply eat them. After a successful hit roll, the target will begin to digest, taking 40,000 acidic damage each turn until either dead, or the avi’yark is defeated/regurgitates them.
Spell Casters: Avi’yark can cast any spell ever… any spell… with the exception of the Summon Shadow Slave spell. They can only cast up to one level below the level used to summon them. Avi’yark summoned with level 33 or higher may often-times use the spell to summon their mate from the shadow realm, bringing a second one of these creatures into the normal realm. They also have access to all Magic Skills.
Transmutation: Avi’yark can transform their bodily form into something more friendly-appearing if they need to, but they are forever cursed with the inky blackness on their body with white eyes. Illusion spells are doomed to fail to hide their ancient branding. Transmuting into another form also gives them their species traits or monstrous skills on top of their own. Stats do not change. They can become anything.
Skill Users: Avi’yark can use any skill at any time that they have the pre-requisites for the skill. After all, they know them all. They know all the fighting arts, too. This is especially useful for when they use Transmutation. They also have access to all Class Skills.
Multi-Vision: Avi’yark have three sets of beautiful eyes, all clouded in wretched white. One set sees in night-vision. One set sees in infra-vision. One set sees with ultra-vision and truesight. Avi’yark are experts at closing sets to see from others, but have no trouble seeing out of all of them at once.
Ultra-Hide: With an incredibly thick hide, this is the source of their Defense and M.Def.
Racial Hatred: Avi’yark enjoy torturing and killing ryzzixi slowly. They will even befriend them, only to shatter their dreams as soon as they are free. They enjoy it when a ryzzixi summons them, because they know that such a creature was made to put them in, and they can be talked into summoning them at full power. At full power, they will take great pleasure in linking themselves, and slowly pulling the arms off of their summoner, cauterizing their wounds with the hottest metals the land has to offer before they even think of searching for a shadow crystal.
Only Weakness: Avi’yark have no defense against light magic, and apply double their perception to the effects.

Base Stats:
Str: 40000 End: 40000
Mag: 12000 Wil: 34000
Spd: 12000 Sth: 16000
Per: 28000 Kno: 10000