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