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