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