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