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