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