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