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