Open Air Parking
Taken Down an helicopter with a car.

At the beginning you will be asked to use your Chaos Form to defeat a large enemy.

Don't do it!

Kill it in your normal form and proceed to the next area. There will be a short cutscene with some big red spikes. After that pickup a car a look towards the sky and throw the car towards the helicopter.
After defeating the large enemy using Chaos Form, just change to the normal form again.
Death Dealer
Meet Vulgrim.


To Move a Mountain
Collect the Earthcaller.


Prison Break
Free Samael from his cage.


Chasm Jumper
Learn Shadowflight.


Reaper
At this point you should have 1000 souls or close to that. Just go to Vulgrim and buy the scythe from him. The achievement should unlock right away.

High Flier.
Kill 5 duskbats without touching the ground. Do this one on the finish kills challenge in Choking Grounds.

Aerial Predator
Right after you defeat Trauma there should be a cutscene after it you will be at the back of the angelic beast. Save your progress in case you dont unlock the achievement after this battle. Just shoot everything you seen and you can kill.

Elemental Thief
Collect the Crossblade


Like A Bat Outta Hell
Defeat Tiamat. Just throw the red bombs to her and then light them up using the crossblade on the torch and them on the bomb.

Slayer
Probably at this point of the game you've already killed more than 666 demons.


Don't Make me Angry.
Unlock the Chaos Form ability.


One tough cookie
Meet Ulthane.


Who's Counting
Kill more angels than Ulthane. After you're first encounter with Ulthane you will fight with him but you will be stoped by angels. After that you will start some kind of race with Ulthane to see who kills more angels. There will be a counter on the top right corner.

Tremor Bringer
As you make your way to the griever you will unock this by smashing a rock with your sword.

Rocked Your Face Off
Defeat the Griever. To defeat this boss you'll have to smash her leg with a train and destroy the blue crystals with the gauntlet. Careful on this because the griever can overheat the crystals and then you can't break them. Best way is to hide behind the train while she uses her laser and then make a run for the crystals.

An old Friend
Collect Mercy. You'll get this as a reward from Ulthane for killing the Griever.


Time Lapse
Acquire the Chronomancer Ability.


Reunited
Obtain Ruin. After the cutscene where you obtain ruin a large number of enemies will spawn so just call ruin and start killing demons from the horseback.

River of Blood
Shed 3000 gallons of demon blood. At this point of the game you should be close to get it. Just keep killing things.

Ashes to Ashes
Defeat the Stygian. Just do has you did to kill the miniboss worm before. This time you have to attack the Stygian head with the sword first because she has some kind of armor on her "face".

Reach Out & Touch Somebody
Obtain the Abyssal Chain


Devastator
Level up the Blade Geyser attack to at least level two (i'd recommend level 3 as it is the only wrath attack in the game which deals any real damage). Go to the iron canopy and enter a room with a lot of spiders. Round them up an just use the attack on them. One room which is exceptionally good for it is the one you pass right before the big seal (before you fight silithia). This room is also good to level up your weapons and farm for souls as you only have to climb back up the growth and dash three times and the spiders will have respawned. If you dind't get the achievement yet just go to the crossroads and gather some zombies.

One Mean Mother
Defeat Silitha. To defeat her you need to get close to her by using the abyssal chain.

Into the Void
Obtain the Voidwalker.


Treasure Chest
Search 150 chests. You should get this one by now.


Paybacks A B****
Defeat Straga. Just use the voidwalker on his club then go on his back and press "E" on that eye thing.

Sight Beyond Sight
Obtain the Mask of Shadows.


Ultimate Blade
Collect all the pieces to forge the Armageddon Blade(max level of chaoseater).


The Final Challenger
Defeat Abbadon/Destroyer. At the first battle one of the dragon's foot will be a ghost state, Attack the other one.

You call that easy?
Beat the game on Easy.


Balance Restored
Beat the game on Normal.


A True Horseman
Beat the game on APOCALYPTIC.

For the collectibles check out Plasma SKX guide.
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=809307407

World Raider
Collect all Artifacts.


Wrath Machine
Collect all of Wrath Powers.


Wrath of War
Collect all wrath cores.


Full Power
Collect the maximum amount of lifestones.


Legendary Form
Collect all armor pieces.

All of this strategies for grinding are from Larkin
Dark Rider
Ride 100 miles. Go to the Soul bridge in the Ashlands and ride through it. Once you are on it all you have to do is press the "back" button and Ruin will turn around at the end and enter the Soul bridge again. Doing this for proximately half an hour will unlock the achievement. So either use a rubber band and pull back the stick on your controller or if you use a keyboard just keep the "back" button pressed down. You can use a pencil which you squeeze under the key that is right above your "back" key.


Battle Hardened
Max level all weapons and unlock all combat moves.
Leveling up your weapons:
The iron canopy is the best place to level your weapons up. There are a lot of rooms containing a huge amount of spiders but one is special since you can make the spiders respawn exceptionally fast. After deafeating Silithia leave the room the way you came. You have to pass two webdoors, then take a left and head down the hole. In the next room round up the spiders on the wall and kill them with your weapon of choice. Now climb back up the demonic growth, dash forward about three times, turn around and re-enter the room. The spiders will have respawned and you can kill them again. Rinse...repeat...
A good idea is to equip "War's Glory" and/or "Combat Lore" as it will enhance the experience gained from every hit. This way you will level all of your weapons up quite fast.

Note/spoiler: You don't need to level up your chaoseater sword as you will get the Armageddon Blade at the end of the game which is already maxed out.

Soul farming:
I'd also recommend going to the iron canopy for that. Equip "Death's Blessing" and/or "Reaper" to maximize the souls you get from every kill and start killing spiders. This way you get a lot of souls quite fast. Another way is to ride the passage which leads to the sandworm area in the ashlands. You will find a lot of Phantom warriors to kill which, if done from ruins back, will count towards the horseman achievement. A third way would be to farm the crossroads. Kill everthing you find there...save...load...and kill it again.
Another way to gain some souls quickly is by killing Wicked K. He is a special character who can be found in four locations throughout the game. You will find him in the Chocking grounds, Drowned Pass, Anvil's Ford and the Twilight cathedral.
Once you collected a lot of souls just enter vulgrims shop and purchase the battle moves of every weapon.

Note: You only have to buy the level one moves.

Improvised Kills
Kill 150 enemies with environment objects. A good place to farm for this achievement is the crossroads. There are a lot of zombies who will instantly die from any environment attack. For other enemies in this area just get their health down and then attack them with something from the environment. It only counts if the killing blow was executed with an environmental weapon.

If you have destroyed most of the environment and this achievement still didn't unlock you can go to the iron canopy. In the room with the bomb thingy on the lift you will meet a lot of spiders. Just use the bombs to punch the spiders or throw it at them. Because the bomb instantly respawns you will have an infinite amount of ammo. But beware...you have to kill the spiders on impact. The explosion doesn't count as environmental kill!

If you have already finished the game and this achievement is still missing, you can just start a new game as the environment kills will carry over.


Horseman
Kill 150 demons from horseback. A good place to farm for easy kills towards this achievement is the Crossroads. Once you have obtained ruin just go back there and kill everything...save...load...and do it again. Another way is to ride the passage which leads to the sandworm area in the ashlands. You will find a lot of phantom warriors to kill. Once you reached the end of the passage ride into the room on the right, turn around and ride back. The phantom warriors will have respawned and you can kill them again.

BFA
Unlock everything.