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