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