PART 1
I believe RPC-115 to be a mediocre and underexplored anomaly, so it would only be fair to give it justice by legitimately making it an intimidating war mongering business man. Say, for instance, here:
The Witch-Doctor crosses his arms, bringing his right hand to his chin. "And what do I give you in exchange?"
"That depends on you. What are you willing to trade for this?"
This reads like a normal conversation. Which is fine! But it could be a lot better. How about you spice it up?
The business man makes five steps forward, his sudden movement startling the followers of the Witch-Doctor. Now face to face, he replies without blinking. ''What are you willing to trade for this?"
Here's another example:
The businessman extends his hand out, and the Witch-Doctor reciprocates the handshake, but upon contact, the Witch-Doctor leans forward and whispers, "You have a dark aura. I see the void beneath your mask, it was revealed to me long ago when I saw the shadow of the black tower."
The businessman whispers back, "There are many avatars of darkness. I know you are one of us too."
Again, this seems like a perfectly normal conversation. How about we tense up the ambient?
The businessman extends his hand out, and the Witch-Doctor firmly reciprocates the handshake. Upon contact, the Witch-Doctor leans forward and whispers, "I see the void beneath your mask, it was revealed to me when I saw the shadow of the black tower. You have a dark aura. "
The businessman whispers back, "I am but one of many avatars of darkness''. He leans back, still whispering while maintaining eye contact. ''I know you are one of us too."
These are but subtle suggestions and minor changes, but observe how quickly tensions rose between the two characters. People can speak with their body alone as well, make use of that and you'll have a Gus Fring wannabe legitimately intimidating character in your hands.
++PART TWO
Dialogues have too many words and too little body language in between. There's no need to chop up the exposition or anything like that, even the slightest hint of emotion could have such an impact on your character.
When they had finally finished punishing him, I came to wrap his body, but he was barely hanging onto life. He looked at me and said-"
Like here, he's just reciting what his old pal said. How much a difference would it make that, after describing such a traumatizing event, he would shed a tear before delivering his speech?
[…] I came to wrap his body, but he was barely hanging onto life. He looked at me and said-". The Witch-Doctor is interrupted by his own restrained sadness, represented by a single tear running down his left cheek. ''He said:''
After his long speech he has this to say
"He died there in my arms. I honored his death for days." Slowly turning around, he then states, "I will not honor any of you."
Short, to the point, but I don't really feel the hatred behind his words. How about something more visceral?
"He died there in my arms. I honored his death for days." Slowly, he cycles his gaze to the guildmembers surrounding him. He points them out with his finger, while his voice cracks as he yells. "I will not honor ANY OF YOU!"
Moving on we reach on what Blairin said, ''Why would you shoot a man before throwing him out of a plane?''
The Witch-Doctor grabs the chieftain, and forces him closer to himself, holding the machete to his throat. "I no longer recognize your authority, guild-master! I have become my own master now, and I will revive the kingdom that you all failed to heal." The Witch-Doctor slays the guild-master, spraying blood over his face and uniform.
Again, how easy it is to convey feelings and emotions with actions more than words? Here's how I would do it, seeing as I have personal experience with machetes and people's heads:
The Witch-Doctor grabs the chieftain by his hair, forcing him closer to himself. His hand is trembling, but its firm enough to raise the machete's edge above the chieftain's neck. "I will rid the kingdom of the darkness that you all failed to heal." The Witch-Doctor forcefully brings the machete down the chieftan's neck. Not satisfied, he raises the machete and strikes down multiple times, spraying blood over his face and uniform. He repeats this several times before finally, severing his head off his body.
Now you could implement something Blairin suggested, ''It would probably be better to portray this maybe as him thinking upon what lead him to the actions of killing the guild as he watches them choke on the gas.''. You can add this to your chapter ending
The Witch-Doctor rises from the ground. As his shaking hand holds the blood-soaked machete, his eyes too are shifting focus between too many things all at once. The severed head of his previous master. His previous guildmates, contorting on the ground, unable to breathe. His followers firing upon those still alive.
The sounds of gunfire ricochet through the dark jungle, announcing the arrival of the War-Doctor.
Now I'm not the best prose writer myself [less so at 1 AM], but this is more or less what I'd do: have less words, more actions. It would make more justice after the long and overdue discussion the Witch-Doctor had moments prior.
++PART 3
Helicopter helicopter
It only got a suggestion, make it bloody and gory.
Those caught in the line of fire become dismembered instantly.
You can always be more specific!
Those caught in the line of fire have their arms, legs, fingers, or heads dismembered instantly.
Next!
Explosions rock the ground and send bodies flying through the air.
It could do something else.
Explosions rock the ground, sending bodies and deadly debree flying through the air.
Overall decent part, but it could use more violence. Nothing too exaggerated, just what you would expect from your average African conflict. Or maybe I'm completely desensitized to violence given that this is but the least violent day in Tamaulipas.
++THE ENDING
I'll tell ya the way Blairin probably intended to: it reads like a Forum post explaining the ending rather than an actual ending. You could make it an allegory about intrusive thoughts, how the darkest imagination of people can come from those with the purest intentions, how personal reason can corrupt our morality, something like that. You did say you don't know how to end it yet, so maybe hint at what became of him rather than explicitly stating it.
You COULD have a scene like this: as he slowly realizes just how unhinged and alone he really is, and the consequences of his actions, have RPC-115 show up AGAIN and make him another deal. It would make great contrast compared to the first time they met, when the doctor said he was an avatar of darkness. If you do, I strongly recommend you tie it together. Have RPC-115 make another offer, relatable to how many times we people say ''just one more time…just one more'' when we are out of control.