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