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