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