Here is the full list of all 66 Torchlight achievements. It takes around 100-120 hours to unlock all of the achievements on Windows.
Beat the game with all three classes
Achieve player level 65
Reach the 50th floor of a dungeon
Do at least 10,000 damage to an enemy in a single strike
Kill 50,000 monsters
Suffer 20 disenchants from the enchanter
Catch 1000 fish
Complete 25 Gar Quests
10 mods used at the same time
5 mods installed at the same time
1 game mod installed
Defeat Ordrak on Hard
Retire two characters
Defeat Ordrak on Easy Hardcore
Gamble 50 times
Retire a character
Defeat Ordrak with no deaths
Defeat Ordrak in 8 hours or less
Defeat Ordrak in less than 5 hours
Complete 200 Quests
Gamble 20 times
Gamble a unique item
Smash 1500 Breakables
Collect 250,000 gold
Have an item disenchanted on the first enchantment attempt
Use 50 potions on your pet
Successfully enchant one item 10 times
Defeat Ordrak on Easy or Normal
Defeat Alric
Have 100,000 gold in your inventory
Catch 100 fish
Permanently transform your pet
Defeat Medea
Take 25,000 steps
Kill 5000 Monsters
Catch 50 fish
Successfully enchant one item 5 times
Defeat Krag
Pull 100 levers
Successfully create 25 items using the transmuter
Defeat the Ember Colossus
Defeat the Root Golem
Transform your pet into a Mimic
Defeat the Overseer
Achieved enlightenment by speaking with the horse 100 times
Change your pet by feeding it fish
Defeat Brink
Equip a spell on your pet
Send your pet to town
Fill your pet's inventory
Blow 25 enemies to pieces with critical strikes
Find the entrance to the mine
Reach level 100
Complete 50 Hatch Quests
Gamble 100 times
Achieve player level 100
Retire over 300 levels worth of characters
Achieve maximum fame
Die 500 times
Kill 25 champion trolls
Defeat Ordrak on Very Hard
Defeat Ordrak on Normal Hardcore
Defeat Ordrak on Hard Hardcore
Defeat Ordrak on Very Hard Hardcore
Drink 5,000 potions
Sell 10,000 items to vendors