Here is the full list of all 119 Torchlight II achievements. It takes around 200 hours to unlock all of the achievements on Windows.
Explode 10,000 enemies
Do 10,000 damage with a single attack
Defeat Cacklespit
Squish 500 critters
Deal 10,000 critical strikes
Defeat the King In Masks
Take 100,000 steps
Break 1,000 breakables
Open 500 chests
Use an enchanter 50 times
Wear a completed armor set
Socket 50 gems into items
Die with a hardcore character
Start a hardcore character
Begin new game plus
Use a map
Defeat the Nether King in Casual difficulty
Defeat the Nether King in Normal difficulty
Defeat the Nether King as an Engineer
Defeat the Nether King
Defeat Vyrax
Find 10 secret rooms
Defeat the Dark Alchemist
Defeat 100 champions
Defeat Killbot
Learn 4 spells
Take 50,000 steps
Defeat Thiss
Defeat Bloatfang
Defeat the Grizzled Alpha
Obtain a tier 2 skill bonus
Defeat the Wraith Lord
Use 500 potions
Defeat Boletus Rex
Defeat the Siege Guardian
Squish 100 critters
Teach a pet 4 spells
Defeat Ezrek Khan
Sell 500 items
Defeat Aruk
Fish 100 times
Defeat the Artificer
Deal 1,000 critical strikes
Defeat the Manticore's Mate
Defeat the Manticore
Fish using dynamite
Defeat Grand Regent Eldrayn
Explode 1,000 enemies
Destroy a socketed gem
Recover a gem from an item
Trade an item with another player
Defeat Chillhoof
Join a multiplayer game
Open 100 chests
Teach a pet a spell
Defeat Mordrox
Take 10,000 steps
Defeat 25 champions
Defeat the Fallen Guardian
Use 50 potions
Add a friend
Start a multiplayer game
Defeat King Pogg
Use an enchanter 10 times
Defeat Kidrik the Mauler
Defeat the Winter Widow
Defeat General Grell
Break 100 breakables
Learn a spell
Obtain a tier 1 skill bonus
Defeat One-Eyed Willy
Explode 100 enemies
Find a secret room
Open 20 chests
Fish 10 times
Send your pet to town
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 Veteran difficulty
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
Purchase 20 items from the gambler
Purchase 50 items from the gambler
Purchase 100 items from the gambler
Have 100,000 gold
Have 1,000,000 gold
Have 10,000,000 gold
Defeat 500 champions
Recover 10 gems from items
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
Obtain a tier 3 skill bonus
Socket 500 gems into items
Use 10 maps
Use 100 maps
Use 5,000 potions
Assemble TrillBot
Defeat Aleera
Squish 1000 critters
Defeat Marishka
Defeat Verona
Find a legendary item
Reach level 100