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