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