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