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