Notes: Used the Monster Manual and the Epic Level Handbook. A bit of tweaking went along with the devil to make him worthy of it's 27 challenge rating.
Advanced Ice Devil (Gelugon) CR 27
LE Huge outsider (Baatezu, evil, extraplanar, lawful)
Init +13; Senses darkvision 60 ft., see in darkness; Listen +45, Spot +45
Aura fear (10 ft., DC 37)
Languages telepathy 100 ft.
AC 38 (-2 size, +6 Dex, +22 natural), 26 touch, 20 flat-footed
hp 631 (42 HD); DR 15/epic and good; regeneration 8
Immune cold, fire, poison
Resist acid 15
Fort +31, Ref +27, Will +28
Spd 30 ft.
Melee +56/+51/+46/+41 +3 unholy, cold iron spear of frost burst (3d6+22, 19–20/x3) and +50 bite (3d6+6) and +50 tail (4d6+6)
Space 15 ft.; Reach 15 ft.
Base Atk +42; Grp +60
Atk Options Power Attack
Special Atk slow, summon baatezu
Spell-Like Abilities (CL 27th) At will—break enchantment, quickened cone of cold (DC 32), dispel magic, fly, greater teleport (self plus 150 pounds of objects only), hellfire, ice storm (DC 31), invisibility, persistent image (DC 32), true seeing, unholy aura (DC 35), wall of ice (DC 31); 1/day—wish
Str 34, Dex 20, Con 28, Int 22, Wis 22, Cha 22
Feats Alertness, Blinding Speed, Cleave, Combat Reflexes, Devastating Critical (Fortitude save DC 43), Great Cleave, Improved Critical (spear), Improved Initiative, Improved Natural Armor, Overwhelming Critical (spear, +2d6), Power Attack, Quickened Spell-Like Ability (cone of cold), Superior Initiative, Weapon Focus (spear)
Skills Bluff +45 (+51), Climb +45 (+57), Concentration +45 (+54), Diplomacy +22 (+28), Disguise +22 (+28), Intimidate +45 (+53), Jump +45 (+57), Knowledge – Arcana +45 (+51), Knowledge – Planes +45 (+51/+53 Hell), Knowledge – Religion +45 (+51),Listen +45 (+51), Move Silently +45, Search +45 (+51), Sense Motive +45 (+51), Spellcraft +45 (+51), Spot +45 (+51), Survival +45 (+51/+53 track)
Possession +3 unholy, cold iron spear of frost burst
Fear Aura (Su) An ice devil can radiate a 10-foot-radius fear aura as a free action. A creature in the area must succeed on a DC 37 Will save or be affected as though by a fear spell (caster level 27th). A creature that successfully saves cannot be affected again by the same ice devil’s aura for 24 hours. Other baatezu are immune to the aura.
Slow (Su) A hit from the tail or spear induces numbing cold. The opponent must succeed on a DC 39 Fortitude save or be affected as though by a slow spell for 1d6 rounds.
Summon Baatezu (Sp) Once per day an ice devil can always summon 2d10 lemures or 1d6 bearded devils, 2d4 bone devils. Or another ice devil with a 50% chance of success. This ability is the equivalent of a 8th-level spell.
Regeneration (Ex) An ice devil takes normal damage from good-aligned weapons and from spells or effects with the good descriptor.