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