Uh… okay, just as a heads-up… I'm really, really picky when it comes to poetry that's supposed to have a repeating meter pattern.
This… doesn't quite get there. You've got some contrived/shakey rhymes, like "creation"/"one". You're assuming that the reader will put the emphasis on the "tion" part of "creation", so it comes off as "cre-a-shun" to rhyme with "one". However, with the line "The crowd admired their brand new creation," I read "creation" as "cre-a-shin" so it didn't rhyme. The fact that there really isn't a recurring pattern of stressed/unstressed makes it hard to figure out the cadence of the work.
Additionally, each line has a different number of syllables/poetic "feet", so it makes it even more unwieldy. For example:
The gathering was a long and hard process. (11)
The deaths of many would not be in vain. (10)
The group once again formed, weaker this time. (10)
Finally, they began to create the pain. (11)
Rebar came first, stringing pieces together. (11)
Concrete then came, embracing the rebar with strife. (12)
The leader stepped forwards, painting an odd face. (11)
They joined hands, blessing their creation with life. (11)
And then towards the end there's no attempt to try for the 11 syllables (why 11, by the way?) and then I'm left wondering why bother with stanzas at the beginning rather than something more free-verse and unrestrained by pattern.
Also, some of the rhymes seem overly contrived, in that the meaning/coherence of the sentence suffers to try and facilitate the rhyming. I don't really understand what's going on at the start. Where did the crowd come from? How is "the dark" left with their tasks? What does it mean to "create the pain"? Pain of what?
Overall, I dunno. Doesn't seem solid as-is, and the poem boils down to (I think?) "some cult made 173 and it killed a bunch of people", which is… not super interesting or exciting, given the other works that have been posted for the 'fest. But then, I'm just super picky about poetry.
last thing—"It began it's rampage once" > you want "its". Only use "it's" if you can replace the word with "it is".
