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