Here is the full list of all 66 Torchlight achievements. It takes around 100-120 hours to unlock all of the achievements on Windows.
Complete 25 Gar Quests
Reach level 100
Smash 1500 Breakables
Achieve maximum fame
Reach the 50th floor of a dungeon
Achieve player level 100
Catch 100 fish
Catch 50 fish
Kill 25 champion trolls
Retire over 300 levels worth of characters
Defeat Ordrak on Hard Hardcore
Suffer 20 disenchants from the enchanter
Achieve player level 65
Defeat Ordrak on Normal Hardcore
Transform your pet into a Mimic
Use 50 potions on your pet
10 mods used at the same time
5 mods installed at the same time
Beat the game with all three classes
Defeat Ordrak on Very Hard
Defeat Ordrak on Very Hard Hardcore
Complete 200 Quests
Gamble 100 times
Achieved enlightenment by speaking with the horse 100 times
Gamble 50 times
Retire two characters
Defeat Ordrak on Easy Hardcore
Do at least 10,000 damage to an enemy in a single strike
Gamble 20 times
Gamble a unique item
Have 100,000 gold in your inventory
Defeat Ordrak on Hard
Defeat Ordrak in 8 hours or less
Defeat Ordrak in less than 5 hours
Collect 250,000 gold
Successfully enchant one item 10 times
1 game mod installed
Retire a character
Successfully create 25 items using the transmuter
Defeat Ordrak with no deaths
Defeat Ordrak on Easy or Normal
Defeat Alric
Defeat Medea
Have an item disenchanted on the first enchantment attempt
Successfully enchant one item 5 times
Kill 5000 Monsters
Take 25,000 steps
Defeat Krag
Defeat the Ember Colossus
Permanently transform your pet
Defeat the Root Golem
Pull 100 levers
Defeat the Overseer
Equip a spell on your pet
Defeat Brink
Change your pet by feeding it fish
Send your pet to town
Fill your pet's inventory
Blow 25 enemies to pieces with critical strikes
Find the entrance to the mine
Catch 1000 fish
Complete 50 Hatch Quests
Die 500 times
Kill 50,000 monsters
Drink 5,000 potions
Sell 10,000 items to vendors