The Great Eye (CR 20)

A huge bulbous orb covered in rune carved chitinous plates with ten tentacles and a body covered in a multitude of eyes hovers menacingly before you. Where a mouth should be are jagged tusks and multiple gill flaps that open and close rhythmically as its singular central eye stares unblinking at you. As its four large tentacles writhe, its two smaller tentacles, each ending in three digit-like protrusions move with grace, gathering arcane energies that coalesce in a globe of flames about to be unleashed with devastating effect. 
XP 307,200
NE Huge aberration (aquatic)
Init +6; Senses darkvision 90 ft., low-light vision, all-seeing; Perception +41

DEFENSE

AC 30, touch 11, flat-footed 27 (+2 Dex, +1 dodge, +19 natural, –2 size)
hp 150 (20d8+60); aqueous regeneration, electricity healing
Fort +13, Ref +10, Will +18
Immune electricity; SR 21
Aura electricity (5 ft., 2d6 electricity)

OFFENSE

Speed 5 ft., fly 30 ft. (good), swim 30 ft.
Melee 4 tentacles +21 (1d8+6)
Space 15 ft.; Reach 15 ft.
Spell-Like Abilities (CL 20th; concentration +26)
Constant—analyze dweomer, read magic, true seeing
3/day—dispel magic (DC 21), passwall, spellcrasher (lesser) (DC 22)
1/day—black tentacles (DC 22), break enchantment (DC 23), siphon magic (DC 23)
Spells Known (CL 18th; concentration +26)
9th (4/day)power word kill (DC 27) 
8th (6/day)rift of ruin (DC 26), stormbolts (DC 26) 
7th (8/day)hungry darkness (DC 25), teleport trap (DC 25), umbral strike (DC 25)
6th (8/day)chains of fire (DC 24), globe of invulnerabilityhellfire ray (DC 24)
5th (8/day)acid spray (DC 23), feeble mind (DC 23), pain strike (mass) (DC 23)spell absorption
4th (8/day)ball lightning (DC 22), charm monster (DC 22), dimensional anchor, hallucinatory terrain (DC 22) 
3rd (8/day)aqueous orb (DC 21), call of the void (DC 21), fireball (DC 21), hold person (DC 21) 
2nd (8/day)daze monster (DC 20), fog cloud, invisibility, resist energy, shatter 
1st (8/day)person (DC 19), comprehend languages, corrosive touch (DC 19), magic missile (DC 19), wave shield (DC 19) 
0 (at will)acid splash (DC 18), detect magic, daze (DC 18), drench (DC 18), light, mage hand, message, open/close, penumbra 

STATISTICS

Str 23, Dex 14, Con 21, Int 20, Wis 18, Cha 26
Base Atk +21; CMB +25; CMD +37
Feats Alertness, Dodge, Flyby Attack, Great Fortitude, Improved Initiative, Intensified Spell, Iron Will, Maximized Spell, Mobility
Skills Acrobatics +22, Fly +22, Intimidate +28, Knowledge (arcana) +35, Perception +41, Spellcraft +30, 
Survival+24, Swim +34; Racial 
Modifiers +8 Perception, +8 Swim, +4 Fly
Languages Aklo, Aquan, Common, Draconic, Undercommon; telepathy 100ft.
SQ amphibious

SPECIAL ABILITIES

All-Seeing (Su) 

A great eye’s central eye allows it to see all things as they really are. The arcane eye is under the constant effect of an analyze dweomer, read magic, and true seeing spell. 

Aqueous Regeneration (Su) 

great eye gains regeneration 4 (healing 4 hit points per round) anytime it submerges itself completely within a body of natural salt water, fresh water, or brackish water. Stagnant, poisoned, or trapped water (such as water within an artificial pit or a bag of holding) does not activate this ability. Great  eyes can heal up to 4 hit points per Hit Dice per day with this ability, after which it ceases to function. 

Electricity Healing (Su) 

Electricity damage heals a great eye 1 point of damage for every 3 points it would otherwise deal. If the amount would cause the great eye to exceed its full normal hit points, it gains any excess as temporary hit points-these temporary hit points last for 2 hours. 

Spells 

great arcane eye casts spells as an 18th-level sorcerer.

Water Breathing (Ex) 

great eye breathes water and can use its spells and abilities underwater.