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