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