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