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