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