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