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