Ok, if that's the case: (Disclaimer, I read the whole thing, but to avoid spoilers, I'll try to stick to examples that are in the beginning.)
1) Redundancy. For example:
You tell the reader "His time is almost up" Then proceed to paraphrase it in the next sentence: "The moment of opportunity Zan had been craving for hours was almost up."
And in the same sentence, "moment" and "opportunity" share the same meaning. Though they are used for different situations, they are technically synonyms, so it's also redundant to put both in the same sentence.
Same thing in your descriptions, "a man of the guard" can just be simplified to "guard" which makes it less confusing to read.
I see this is a common mistake, as you also do the same when describing his feeling towards death, and other things. It might be good to remind the reader of these things, but not in the same chapter. However, this problem is a pretty easy fix, so don't worry too much about it, you just gotta practice a bit more.
2) Sentence structure: Some of the sentences go against the logical flow, for example:
"The moment of opportunity Zan had been craving for hours was almost up"
When you break it down, you have 2 ideas that are being mashed into the same sentence.
1: This was the moment Zan had been craving for (here the focus is on Zan, as he is the main subject of the sentence)
2: this moment is almost up. (Describes moment)
If you want to link something like this, go through the word that the 2 ideas share in common, "moment".
so rearrange your ideas:
1: Zan had been craving for this moment (here, the main subject shifts to this moment, as Zan becomes secondary)
2: this moment is almost up (Describes moment)
Add in a little flair and dramatize it, and you get: "This was the moment/opportunity that Zan had been craving for, but it was almost up.
Of course, you can write it in diferent ways and get the same effect:
"Zan had spent hours craving for this opportunity, which was almost up."
"This was the opportunity of a lifetime, but his time was almost up." (you can spit it into 2 "sentences" like this using a comma conjunction as well, which links and partitions the ideas)
You can choose whatever you think fits, as long as the idea matches up with the logical flow. Use the example above as a rough guide, and once you get the hang of it, it will help the flow of the story. If you want to learn more, just search up independent and dependent clauses, and how to use them.
3) Integrate your descriptions into the character's actions
I won't go into this as much, as it's more of a style thing, but I would recommend that you try to integrate descriptions into your character's actions. It's not necessary, but its helpful for when you have too many to put down.
For example, I'm guessing your MC has green skin, so something like: " He stretched his arms, his skin giving off a green sheen, and got ready for the mission" Or, "His blue eyes turned towards the man and widened."
Your narration is pretty good. Just try to focus on one idea/character at one time. For example, you're talking about Zan and how his time is almost up, then it suddenly goes into a decription of a dead guard laying on the ground, and Zan's numbness to death.
It's a bit off topic, since the reader want to know what's happening with the opportunity and what Zan's gonna do with the limited amount of time.
It seems like you wrote the "time is almost up" just for the sake of having a interesting hook and not for the plot, so you can easily fix this by getting rid of it and making the guard's death as the hook, which works just as well.
Just work on the things above, your descriptions are good, and your content seems pretty interesting. You do a pretty decent job at giving what is necessary, but I would double check. It definitely has potential as a story, and once you fix the main issues, your flow and narration will be much better, making your story into a great one.