Shadows of the Damned

This solution is based on defeating Fleming on the Legion Hunter difficulty:

There are three main stages to this boss fight, much like all the other previous boss fights in the game.

Stage 1:

The first stage is the most easiest as Fleming only fires his laser at you, pounds the ground, opens up his trench coat to reveal Paula and coats the area in darkness. Each attack can avoided and when Fleming decides to reveal Paula, this is the perfect time to have a drink, charge up the HotBoner, reload any weapon or go pick up some more ammunition.

During the first stage of the boss fight, any particular weapon can work well causing damage to the boss. However, I strongly do not recommend using the Dentist due to the fact it can be difficult to judge whether or not Fleming will open his trench coat. Anyway, fire away at the Fleming, his face, his chest, anywhere can be shot at to infect damage on the Lord of Demons. Once the boss has taken enough damage, Fleming will go into a slump and a few yellow cracks appear on his body; this is your cue to hit him with a Hot Boner bomb.

If successful, Fleming splits into three pieces and begins floating around the room. Pull out Dentist, lock on to the body part that is glowing red and fire away. If you have locked on successfully the red body part should be dealt with approximately three quarters of a clip from the Dentist.

Stage 2:

In the second part of the boss fight, Fleming unleashes a second more powerful laser and sometimes in cases himself within a green barrier. The second laser beam can still be avoided, however be careful as Fleming tries to lock on to you or follow you while performing this attack. This particular laser beam only last for a few seconds, so just keep on dodging.

In between breaks of drinking, dodging, gathering ammunition and shooting the lamp whenever it gets dark, just keep on hitting Fleming with everything you have just like in the previous stage. Eventually, Fleming will in case himself in a green barrier and that's you cue to pull out the Skullblaster, charge it up and fire off a Skullblaster bomb in one of the openings in the barrier. This explosion should be enough to make Fleming slump again with the yellow cracks. So like before put a Hot Boner bomb on the boss causing Fleming to split into three parts and then fly around the room again.

Again, I recommend using the Dentist to lock on to the red body part and again approximately three quarters of a clip from the Dentist should be enough.

Stage 3:

Now, things can get a bit annoying or become a diamond in the rough as Fleming unleash a new attack. The boss open up his trench coat and a Darkness hand flies at you and if it is successfully in grabbing you, pulls you into a darkness filled room containing two or three demons, two hearts, a drink and three doors that need to be open with a Hot Boner bomb.

This darkness room is the only part of the boss fight where you can stock up on drinks if you need to and I'm sure some people might. So, if the darkness hand grabs you, don't worry. Once you are in the room, just dodge past the demons in the room, grab a heart, grab the drink and then fire off a Hot Boner bomb at one of the doors and hope that the door you picked leads you out of the room and back to the boss fight with Fleming.

Once you are out, continue to fight Fleming as you have been in the previous boss stages. However, when Fleming in cases himself in the green barrier and you fire off a Skullblaster bomb in one of the openings in the barrier. Fleming should slump again, but this time the yellow cracks don't appear. But don't worry, the game isn't glitched. Sure, he is slumping over but he hasn't taken enough damage to make the yellow cracks appear.

So, during this slumping period. Pull out the Dentist, lock on to Fleming and just keep on firing. Now, if you have an eagle eye you might see that a red transparent circle comes out of Fleming when he gets up from being slumped. From a certain point of view, his health just got recharged basically. Don't worry, just keep on firing at Fleming with the Dentist until you empty the clip or you have to dodge his first attack after getting up from being slumped for the first time.

Now, it's really time to hit Fleming and not let up. I recommend switching the Skullblaster and charging the gun up to just two or three skulls and letting fly. After a continuous and successful barrage from the Skullblaster, Fleming will slump again and this time the yellow cracks in his body will appear. So like before put a Hot Boner bomb on the boss causing Fleming to split into three parts and then fly around the room again.

Again, I recommend using the Dentist to lock on to the red body part and again approximately three quarter of a clip from the Dentist should be enough. That was the last red body part and Fleming can't take any more and starts to explode. A black hole will appear and demon remains fly out. So, just dodge the demon remains until the chaos is over.

If you are not successful in your onslaught against Fleming, he will eventually in case himself again in the green barrier. You will have to fire off a Skullblaster bomb in one of the openings in the barrier again. Fleming should slump again, but the yellow cracks won't appear and you are basically back to square one.

Note: Based in my style of gameplay, I believe it is the amount of damage you cause with the Dentist to Fleming once he gets up from being slumped for the first time and powerful two or three skull consistent shots from the Skullblaster. I don't believe the third stage of the Fleming fight is glitched. The boss just needs to be dealt a lot more punishment than before. But, in the right way. I do not believe that by placing Hot Boner bombs on Fleming while he is not in a slumped state is ideal since I have seen some of my bombs disappear off of his body after he performs a random attack.

Just like the description says, you'll get this achievement by defeating Fleming. An easy 20 G's, but it is tedious.

Fleming has a few attacks where he will shoot lazers at you from his eyes and stomp the ground. Avoid these by dodging . He will also bring you into the darkness, simply shoot the goat's head swinging above. Fleming will also incase himself in a green barrier. Charge up your Skullblaster and launch the bouncing grenade inside the barrier to destroy it and leave him stunned. Later on in the fight he will send a large hand out to grab you and pull you into darkness, unless you dodge it, you will then have to blow up one of three doors to find which one is leading to the light and then step through- it will bring you back to the fight against Fleming.

Basically, fire upon Fleming's body, you'll soon see his armor begin to crack and he'll eventually become frozen for a few seconds. ( Be careful when firing, he will open up to reveal Paula, shoot at her enough and you will have to restart.) While he is frozen, fire the sticky bomb onto his body and shoot it. Fleming will be blown into three pieces.
His body parts will soon begin to rotate around the room, one of them will be glowing red. This is your target. I found it easy to use The Dentist to fire at the body part since it can lock on. After you have defeated the target, Fleming will reassemble himself. You'll basically repeat these steps until you have defeated all three body parts in turn destroying Fleming.

My first attempt to destroy Fleming was on Legion Hunter, so it was a bit frustrating, he didn't break 3rd time (yellow cracks didn't show up, or they were for only 2 seconds - too little time to deploy sticky on him). Reason is one -this *&%^$ is glitched...
After few tries I've found one solution that really helped me. When you're done with destroying second part of his body, and destroying his green shield, put a sticky bomb on him (neck or head is the best) but DON'T SHOOT IT!!!! Switch to Green Weapon and keep shooting him, but don't aim at the sticky bomb!
It succeeded on my second attempt, yellow cracks showed up once again (long enough) and I was ready to deploy my sweet sticky on him:D
And general TIPS on fight on Legion Hunter (good also with lower levels):
Use green weapon all the time, switch to red only to shoot the goat or deploy sticky bomb, and blue when you need to destroy his body parts.
Oh, and main thing - all my upgrades went to increase damage of green and blue weapons, rest on health and capacity of these weapons.
With this technique I was able to tear him apart in less than 8 mins (first two parts) and about 15 last one.
Enjoy, I hope it helped:)

This guide is for people who are struggling with Fleming on Legion Hunter / Hard difficulty. For general tips on how to beat Fleming see the other solutions. As you probably know by now, Fleming has 2 stagger phases.

Red phase stagger: usually triggered in stages 2 and 3 of the boss fight after shooting a bomb in the green shield. This is not a bug/glitch, it simply means you haven't dealt enough damage yet. You can refer to it as a knock-out

White phase stagger: Triggered at any point during a stage when you dealt enough damage.

Note: For simplicity reasons and to get my point across, suppose the stagger phase lasts 6 seconds in total

When you trigger the Red phase stagger on Easy/Medium difficulty you can keep shooting him for the 6 seconds before he recovers. Shall you reach the damage threshold during the Red phase stagger, his body turns white, indicating it's time for a light bomb. If you happen to pass the 6sec mark, Fleming turns back to normal, BUT any subsequent shot will White phase stagger him again. Giving you unlimited attempts to split his body.

This is not the case on Legion Hunter/Hard difficulty. When you Red phase stagger Flemming and deal enough damage to cause White phase stagger on the 5th second, you only have 1sec left to split his body. Shall you fail to split Fleming's body when White phase stagger is active, Flemings health resets and you're back to square 1.

Strategy for phases 2 and 3: Keep dealing as much damage as possible, takes about 6-7 green bombs to reach the threshold. Use the green shields to stagger. DO NOT DAMAGE FLEMING WHILE HE IS IN RED PHASE STAGGER. You risk reaching the threshold for White stagger and resetting his health. Instead, charge your green bomb and wait for fleming to recover (let the 6sec pass) (make him hang there for 6 sec like a limp di*k) before shooting the bomb. This way, when you cause the White stagger you have the full 6 sec to split his body. Again, shall the 6sec pass and Flemming recovers, his health resets.