A pair of frozen, multifaceted eyes coldly judge all before this towering, insectile monstrosity.
Source: Planescape Monstrous Compendium Appendix I
Technically they are not devils in 2nd edition Advanced Dungeons & Dragons. They are Baatezu. In all other editions they are Devils so that is what they are to me. The Gelugons are high level opponents commonly known as Ice Devils. They guard the eighth level of the Nine Hells. Cania is the frigid layer that protects the only portal to lowest level of the depths of Hell.
Gelugons are the ultimate guardians of Hell. Despite dwelling in the frigid cold of Cania they actually dislike the cold and prefer the hotter layers. They are loyal soldiers of their dark masters. One day they hope to be promoted to a Pit Fiend. After serving 777 years with an unblemished record they are eligible for promotion.
Now promotion kinda sucks. If they are selected to be a Pit Fiend they must endure the Pit of Flame. There they are tormented for 1,001 days. After nearly three years of torture they emerge as Pit Fiends.
The Ice Devils are known to be the most stoic of all devils.It is rumored that inside their chest is a heart of a frozen mortal. This allows them to make decisions without any emotions.
Combat: In AD&D 2nd Edition the Gelugons are high level opponents. They are worth 19,000 experience if defeated.
-Strong like Bull: Gelugons are extremely strong and possess a 18/76 Strength. They attack four times a round with two claws, pincers, and tail.
-Numbing Cold: If struck by the tail of the Ice Devil the victim must save vs. paralyzation or be paralyzed by numbing cold for 1d6 rounds. One in four Gelugons carries a long spear and it can direct it's numbing attack through the spear. A failed save slows(as the spell) the victim for 2d4 rounds.
-Spell-like Abilities: At will detect invisibility(always active), detect magic, fly, polymorph self, and wall of ice.
-Gate: They can attempt to gate in allies. 2 to 12 barbazu with a 50% chance once a day. 2 to 8 Osyluth with a 35% chance one a day. 1 to 2 Gelugons with a 20% chance.
-Regenerate: Ice Devils regenerate 2 hit points per round
-Senses: Gelugons see perfectly in the dark.
-Fear: The Ice Devil radiates a 10ft radius fear aura. All within the aura must save vs rod, staff, wand or flee in panic for 1d6 rounds.
-Misc: 50% Magic Resistance and a +2 or better weapon to be hit.
If by chance you are wandering around in Cania and trying to get to Lucifer's palace....the only entrance is guarded by 9,999 Gelugons. Just make sure you bring a large army of Angels with you.