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