Chided by a lesser warrior, Mawgath seethed, the glow of his chest panel piercing the sludge which now decorated his armor. His massive chest rose and fell with labored breaths, the mired colossus struggling to gather the poise necessary to escape this mess – and finish off the squid.
“Peace is a lie. There is only passion,” he muttered, trembling syllables nearly silenced by the bubbling of the swamplands. Perched and self-satisfied, Lexiconus Qor watched his would-be assassin begin to relent, black eyes now hidden beneath mottled grey eyelids.
“Ah, are we trying patience on for size, ancient one?”
Beard-like tentacles stirred, the stoic humor of the Gray Jedi infuriating the bog-ridden Tarenti.
“It suits one with your lifespan quit well, immortal,” Lexiconus jested, now leaning against the petrified trunk of a great gnarltree. The slow crawl of mold beneath him did not seem to disturb the Quarren in the slightest, who felt a great connection with the humid quagmire.
“Through passion, I gain strength,” Mawgath growled, feeling his rage pool into a font of dark potency. His hatred for his foe, who so easily outmaneuvered him, fueled his broken body. His descent into the sullen earth slowed, mitigated by his concentration – however ireful.
“Through strength, I gain power. Through power, I gain victory. Through victory, my chains are broken”
The Pau’an trailed off, his steel-shelled jaw rising from his chest. Cavernous eyes snapped to life, the Force coursing through furrowed flesh.
“THE FORCE SHALL FREE ME!”
Impossible steps launched the Dark Jedi into a bounding leap, which carried his armored frame from the swamp and onto the Quarren’s dreary mesa. Lexiconus responded with a surprising finesse, the crack of his lightsaber blade goading Mawgath into wild rage. His gauntlets fell with deadly force against an invisible barrier, and from behind the ghostly bastion, Lexiconus prepared to land the killing blow. He would wait for Mawgath to tire…
…but it never came. The Gray Jedi shifted to create space between himself and the groaning tyrant, winding up for the penultimate strike. Mawgath refused to let such tactics deter his assault a second time.
“I will crush you!”
He bellowed as he lifted the earth-stained boulder, drenched flora-husks and swarming insects trickling from its filthy underbelly. Lexiconus easily avoided the massive projectile, clambering over the rocky banks and sinking into a defensive posture.
“Your darkness limits you, Sith,” the Quarren advised. He was simply educating his opponent, who now called his lightsaber to his grasp with a telekinetic gesture.
“Darkness has no limits, squid,” Mawgath spat, his crimson blade lighting the ground beneath.
“It is all around us. It grows, spreads, into the cracks and beneath the surface of our perceptions. It is irresistible, and never gone for long. Darkness is eternal, and this is the power of Death!”
The final syllable was accentuated by the mincing of blades yet again, and even the Quarren held no illusions about what would happen now. Exhausted and outclassed, the Gray Jedi could not stir himself to madness – not even to save his own life – for he felt no terror. The Tarenti scowled as he beat Lexiconus down, struggling to grasp a satisfaction which never arrived.
As the killing blow was struck, tearing the Quarren’s orange hide asunder, he did not fear death. His consciousness ceased, leaving only the darkness which Mawgath so worshipped - one which would never give him the closure he sought.
Lexiconus Qor died in that swamp, never succumbing to the terror which his murderer tried so desperately to inflict – and so it was that another passed into the Force, their death as hollow and as silent as the fallen logs of Dathomir.
Syntax
It sinks, it sank, it had sunk. In this case it’s “the mud sank further”.
The subject here changes abruptly from swamplands to Lexiconus in the same sentence. It might read more naturally if “Bubbling, brewing and fluctuating away” was joined to the previous sentence rather than to this one.
You correctly use a comma to end your thought quote here, but the “he” that followed didn’t need to be capitalised. This counts also for speech quotes.
This is still, effectively, a single sentence, despite the exclamation mark ending the speech quote. The exclamation mark is merely standing in for a comma, so the article “a” following it needs to be lower case. These are just two examples. In this post you consistently capitalised the word following a speech/thought quote without it needing to be capitalised (unless it was a proper noun like Lexiconus, of course).
I’m taking this as a Syntax error rather than a Realism one, because it seems to be just a poor choice of verb tense. The form “was crushed” indicates an action that has happened at a specific time, meaning that the neck is crushed by the time the reader gets to this line. The form “was being crushed” might fit better with the meaning of this line, because it indicates an action that is ongoing as you are reading the story.
Realism
While we don’t have a CS for the creature that attacked Mawgath, your description tells us that it was strong enough to resist Mawgath’s attempts to free himself and that it was slowly suffocating him. Mawgath is physically very robust, but even he can’t ignore the necessity of respiration after his lungs have been starved of oxygen. Going from constriction to roaring without a pause makes for a minor break in suspension of disbelief.
Story
You did a great job presenting the characters and painting a picture of the venue in this post. You gave a concrete reason for Lexiconus being on Dathomir, and that helped to set the scene, but in the end this introduction had little bearing on the rest of the story (i.e. if you had started from ”Get off me snake!” it would have made virtually no difference to the plot of the story).
Another important factor to consider within each ACC post is combat. Here, you wrote a good introduction to the venue and characters, but you dedicated only three short lines to the actual conflict between the two protagonists, and you end the post before the two actually clash. This is a Story detractor because it means the central element of an ACC post, the combat between the two protagonists, has been ignored.