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