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