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