Kill the Shock Widow
While exploring the Spider Caverns, you'll eventually run into an entrance with a boss skull on it, inside is the Shock Widow. You can reach the Spider Caverns from two separate locations on Hammer Island, the Wolf Cave or the Prison (after freeing Ria).

Defeat Barrington
While exploring the Thieves Tower, on the third floor you'll eventually run into an entrance with a boss skull on it, inside is Barrington. In order to access the Thieves Tower, you must first star the "I'll Be The Hooker" quest from Garth located northwest from the Royal City of Adventurine (1 on map). From there he instructs you to go meet his friend Kalia south of the Royal City of Adventurine (2 on map). Once you have started "Dack Unmasked" quest from Kalia, you will be instructed to use a secret entrance to the Thieves Tower that Kalia gives you the code for (3 on map).

Defeat the Judge
North of Sild there is a dungeon called The Obsidian Spire, the Judge is located there from an access point on the fourth floor. Note: There are two different up paths on the fourth floor, one leads to floor five towards Doombringer and the other leads to the Judge.

Defeat Blight
Blight is the final boss of the game. He is located at the top of Castle Superbia. In order to climb the final staircase, you must destroy the cubes located on the top floor. Achievement will unlock as soon as your have defeated him.

Defeat Dace
In order to defeat Dace, you must head to the Wishless Resting Place located in south Fallowfields.
Once inside, you must work towards joining the Children of Sai and progressing down the tombs.
You will eventually reach a chamber where you will find the boss icon, head down the stairs to fight Dace.

Defeat and Restore Malgar to Her Former Glory
There is a lot of preparation for defeating Malgar for good. You must first acquire Agnessa's Medallion in order to permanently defeat this boss which requires you to progress to a certain point in the main storyline. You'll pickup a quest called "Faux Orbuculum" and be instructed to head to Jyn at the southwest of Fallowfields to have her tell you your fortune (1 on map). From there you will be given a riddle, which leads you to the blacksmith in the Royal City of Adventurine (2 on map). Return to Jyn and go into her cellar and obtain Agnessa's Medallion. While it is optional in defeating Malgar, you can help clear the fog by finding The Loop of Light in the Wishless Resting Place in the south of Fallowfields (* on map). If you wish to find it you must dig it up with a shovel inside. If you do not want that, or have succeeded in obtaining it, you must push forward and defeat Malgar (3 on map). Once defeated, place the amulet around her neck and she will be permanently defeated.

Defeat Doombringer
North of Sild there is a dungeon called The Obsidian Spire, Doombringer is located there from an access point on the fourth floor that leads to an empty fifth floor with an access point to the roof where you fight the boss. Note: There are two different up paths on the fourth floor, one leads to floor five towards Doombringer and the other leads to the Judge.

Defeat Sinkage
On Hammer Island at the start of the game you will be instructed to go to the Pirate Hideout. In order to progress to the mainland you must first defeat Sinkage.

Train to Adept Tier
After beating Sinkage and being granted the ability to sail away from Hammer Island, you will first sail to Switch Town. Located there is the Adept Trainer and for 1500 gold they can train you to Adept allowing you to acquire new skills with skill points and to wear better gear.

Train to Expert Tier
After reaching the Royal City of Adventurine, you can locate the Expert Trainer near the center of town. Level 15 and 5000 gold is required to train you to Expert allowing you to acquire even more new skills with skill points and wear the next tier of gear.

Train to Master Tier
On your search for Captain Danielle Skinner, you will exit the caverns into Blackbarrow and locate Skinner's Griffin, up the way a little bit is the Master Trainer. Level 30 and 10000 gold is required to train you to Master allowing you to acquire all of the skills in your skill tree and wear all gear.

Reach Level 50
Upon reaching Level 50, you will unlock this achievement, and as it states there is no more levels after 50.

Beat the game on Hard
Written in the description exactly how is it meant to be unlocked, complete the main questline as the Hard difficulty. After defeating Blight and finishing the dialogue with King Roland, you will finish the game and the achievement will unlock. Unfortunately, beating the game on Serious difficulty does not unlock the achievement for beating the game on Hard difficulty.

Beat the game on Serious
Written in the description exactly how is it meant to be unlocked, complete the main questline on the Serious (hardest) difficulty. After defeating Blight and finishing the dialogue with King Roland, you will finish the game and the achievement will unlock. Unfortunately, beating the game on Serious difficulty does not unlock the achievement for beating the game on Hard difficulty.

Beat the game as Ranger
Written in the description exactly how is it meant to be unlocked, complete the main questline as the Ranger. After defeating Blight and finishing the dialogue with King Roland, you will finish the game and the achievement will unlock.

Beat the game as Warlock
Written in the description exactly how is it meant to be unlocked, complete the main questline as the Warlock. After defeating Blight and finishing the dialogue with King Roland, you will finish the game and the achievement will unlock.

Beat the game as Rogue
Written in the description exactly how is it meant to be unlocked, complete the main questline as the Rogue. After defeating Blight and finishing the dialogue with King Roland, you will finish the game and the achievement will unlock.

Beat the game as Paladin
Written in the description exactly how is it meant to be unlocked, complete the main questline as the Paladin. After defeating Blight and finishing the dialogue with King Roland, you will finish the game and the achievement will unlock.

Beat the game as Wizard
Written in the description exactly how is it meant to be unlocked, complete the main questline as the Wizard. After defeating Blight and finishing the dialogue with King Roland, you will finish the game and the achievement will unlock.

Kill 500 Boars
Boars are most commonly found in west Fallowfields.

Kill 1000 Archons
Archons can be found in The Obsidian Spire in northern Blackbarrow.

Kill 25 Crabs
In the Royal City of Adventurine, you can use the Carriage to travel to a place called Ambrose Retreat. Once you have cleared the defenses of Lockdey in the main questline, you can access a ship at Ambrose Retreat to sail to a location called Summer Keys. Once you arrive search around and kill crabs. I had to leave, sleep and come back to get my 25 kills.

Kill 100 Frost Beetles
Frost Beetles can only be found in the cavern located in Astral Heights. To get there you must take the Griffin, located north of the Resistance secret entrance in the church, to a location called Brisk Observatory.

Kill 1000 Wasps
Wasps can be found in both southern and northern Fallowfields, as well as Blackbarrow.

Kill 1000 Pirates
Pirates are one of the first enemies that you fight. To my knowledge, you can only fight pirates on Hammer Island.

Kill 250 Shamblers
Shamblers can be found fighting the trolls inside the caves leading to Blackbarrow.

Kill 1000 Thieves
Thieves are located in the Thieves Tower, who would have known?

Kill 1500 Wolves
Wolves are probably the most common enemy type, maybe beetles, but I feel like it is wolves. They can be found on Hammer Island, east Fallowfields and in Blackbarrow.

Kill 500 Trolls
Trolls are found in the caves in north Fallowfields, some can be found in the mountain caves, but if you're looking for quantity head to Blackbarrow Hallows located in northern Fallowfields.

Kill 3000 Horde
Horde are the undead. Most commonly found in the Wishless Resting Place, but you can run into them at cemeteries at night and in the corrupted Ruins of Malgar.

Capture Archibald
In order to unlock this achievement, you must first progress through the main questline until you receive "The Lord Award" quest. Proceed into Castle Superbia Throne Room and defeat his knights in order to capture him.

Obtain and Equip any potion.
One of the first NPCs you will come across on your run to Haart's Landing is the potion crafter.
If you complete her quest, you will acquire a potion, if you have auto-equip on then you should get the achievement. If not, equip the potion to unlock the achievement.

Win a game against someone in the card game Walls of Gadir.
Walls of Gadir gamblers can be found all over the world, play them and win to unlock the achievement.

Kill the crypt cat nine times.
Once you join the Children of Sai, located in the Wishless Resting Place, you will come across a vendor and questgiver. There is a cat located there, kill it nine separate times to unlock this achievement...and to become a monster.

Change the colors of your dress.
To my knowledge, there is only one tailor in all of the game to alter your character's gear color. They are located in the Royal City of Adventurine.

Enter the Wishless Resting Place in south Fallowfields.
This achievement unlocks by simply walking in the front door of the Wishless Resting Place.

Have Jyn tell you your future.
Located in southwest Fallowfields, near the edge of the map. You will get this by progressing the main questline.