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