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
Drink 5,000 potions
Catch 1000 fish
Kill 50,000 monsters
Reach the 50th floor of a dungeon
Complete 25 Gar Quests
Complete 50 Hatch Quests
Transform your pet into a Mimic
Sell 10,000 items to vendors
Smash 1500 Breakables
Die 500 times
Kill 25 champion trolls
Achieve maximum fame
Suffer 20 disenchants from the enchanter
Catch 100 fish
Defeat Ordrak on Easy Hardcore
Use 50 potions on your pet
Complete 200 Quests
Defeat Ordrak on Normal Hardcore
Catch 50 fish
Retire two characters
Defeat Ordrak on Hard Hardcore
Gamble 100 times
Gamble 50 times
Gamble 20 times
Gamble a unique item
Achieved enlightenment by speaking with the horse 100 times
Retire a character
Retire over 300 levels worth of characters
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
Collect 250,000 gold
Successfully enchant one item 10 times
Beat the game with all three classes
Successfully enchant one item 5 times
Do at least 10,000 damage to an enemy in a single strike
Achieve player level 100
Achieve player level 65
5 mods installed at the same time
10 mods used at the same time
1 game mod installed
Permanently transform your pet
Defeat Ordrak on Easy or Normal
Defeat Alric
Have 100,000 gold in your inventory
Defeat Medea
Kill 5000 Monsters
Defeat Krag
Take 25,000 steps
Defeat the Ember Colossus
Have an item disenchanted on the first enchantment attempt
Pull 100 levers
Defeat the Root Golem
Successfully create 25 items using the transmuter
Change your pet by feeding it fish
Defeat the Overseer
Fill your pet's inventory
Equip a spell on your pet
Send your pet to town
Defeat Brink
Blow 25 enemies to pieces with critical strikes
Find the entrance to the mine