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