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