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