Avalanchion is located in Avalanchion's Vault in Deepholm. He is the target of the quest  Bring Down the Avalanche.
Prior to the Cataclysm, Avalanchion was part of the periodic Elemental invasions. He spawned in Azshara amidst a host of rock elementals and was constantly escorted by Thundering Invaders.
Avalanchion is eventually sent by Therazane to aid the Earthen Ring in their fight against the Burning Legion.
Avalanchion no longer drops any loot. During his previous appearance in Azshara, he dropped the following:
This section concerns content exclusive to World of Warcraft.
- On attacked
- Do me know you? No matter. Me crush your bones!
- On death
- NOOOOOOOOOOOoooooo..... not again!
This section concerns content exclusive to Cataclysm.
- During the elemental invasion, on appearing
- You be too scared! Me find you!
- During the elemental invasion, on death
- What?! You no can beat me! Me will return!
This section concerns content exclusive to Legion.
- <The deep, thundering words of Avalanchion rumble out slowly as he speaks> Stonemother... send me to help Farseer... Say crush demons... protect <class>. Avalanchion go with Farseer... make demons cry.
- What is it?
- I greet you.
- I obey.
- What do you need?
- I await your command.
- You confuse me!
- WHAT ARE YOU DOING?!
- YOU'RE MAKING ME ANGRY!
- I WILL CRUSH YOUR BONES!
- I am the mountain.
- As you command.
- I am ready.
- His name comes from an avalanche which is a rapid flow of snow or rock down a slope, from either natural triggers or human activity.
- ^  Champion: Avalanchion