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