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