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