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