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