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