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