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