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