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