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