Here is the full list of all 119 Torchlight II achievements. It takes around 200 hours to unlock all of the achievements on Windows.
Use an enchanter 500 times
Defeat Aleera
Defeat Verona
Defeat Marishka
Defeat the Nether King as an Engineer
Find 100 secret rooms
Have 10 friends
Obtain a tier 3 skill bonus
Use 10 maps
Have 1,000,000 gold
Assemble TrillBot
Deal 100,000 critical strikes
Break 10,000 breakables
Find a legendary item
Begin new game plus
Defeat the Nether King as a Berserker
Defeat Cacklespit
Use an enchanter 50 times
Use a map
Defeat the Nether King in Casual difficulty
Defeat the Nether King in Elite difficulty
Defeat the Nether King in Normal difficulty
Defeat the Nether King in Veteran difficulty
Defeat the Nether King as an Outlander
Defeat the Nether King
Defeat the Dark Alchemist
Obtain a tier 2 skill bonus
Defeat Killbot
Defeat Vyrax
Purchase 100 items from the gambler
Defeat Thiss
Defeat Bloatfang
Defeat the Grizzled Alpha
Defeat the Wraith Lord
Sell 5,000 items
Purchase 50 items from the gambler
Socket 50 gems into items
Squish 1000 critters
Recover 10 gems from items
Use 500 potions
Defeat Boletus Rex
Purchase 20 items from the gambler
Defeat the Siege Guardian
Defeat Ezrek Khan
Learn 4 spells
Defeat 500 champions
Defeat Aruk
Defeat the King In Masks
Deal 10,000 critical strikes
Explode 10,000 enemies
Teach a pet 4 spells
Use an enchanter 10 times
Squish 500 critters
Find 10 secret rooms
Have 100,000 gold
Fish 100 times
Do 10,000 damage with a single attack
Wear a completed armor set
Take 100,000 steps
Defeat the Artificer
Defeat the Manticore's Mate
Defeat the Manticore
Defeat Grand Regent Eldrayn
Teach a pet a spell
Open 500 chests
Recover a gem from an item
Destroy a socketed gem
Break 1,000 breakables
Deal 1,000 critical strikes
Take 50,000 steps
Defeat Kidrik the Mauler
Defeat 100 champions
Defeat Chillhoof
Squish 100 critters
Defeat King Pogg
Explode 1,000 enemies
Sell 500 items
Find a secret room
Use 50 potions
Trade an item with another player
Add a friend
Defeat the Winter Widow
Defeat General Grell
Socket a gem into an item
Join a multiplayer game
Defeat 25 champions
Defeat Mordrox
Open 100 chests
Take 10,000 steps
Obtain a tier 1 skill bonus
Explode 100 enemies
Fish 10 times
Defeat One-Eyed Willy
Learn a spell
Break 100 breakables
Defeat the Fallen Guardian
Send your pet to town
Start a multiplayer game
Open 20 chests
Defeat the Nether King with each of the 4 classes
Defeat the Nether King as an Embermage
Defeat the Nether King in hardcore mode (casual)
Defeat the Nether King in hardcore mode (elite)
Defeat the Nether King in hardcore mode (normal)
Defeat the Nether King in hardcore mode (veteran)
Fish using dynamite
Fish 1,000 times
Have 50 friends
Die with a hardcore character
Start a hardcore character
Have 10,000,000 gold
Recover 100 gems from items
Destroy 10 socketed gems
Destroy 100 socketed gems
Sell 50,000 items
Socket 500 gems into items
Use 100 maps
Use 5,000 potions
Reach level 100