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