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