For some odd reason, my most recent collab between the users : @solarfiction and @dacylinder17 has been removed by the Newgrounds Moderation Team. I do not know why that is, as it was a simple birthday gift for a friend of ours but I am most likely not gonna push on.
The collab will be eventually reuploaded either to the SolarForums as a seperate thread or on the Newgrounds Security Crew website.
Yatsufusa
You can "probably" find the reason in the rules:
https://www.newgrounds.com/wiki/help-information/content-submission
If you are still unable to determine the cause, you can ask in the forums or ask _one_ moderator directly:
https://www.newgrounds.com/wiki/help-information/site-moderation
However: 'Do not take the piss.' After reading the rules, you 'should' have a solid idea...
Pyxron
Thank you for linking those. Anyways I did my research, specifically in the "Art" section as it was on the Art Portal.
Ownership : Was the Collab organizer, everyone was credited and agreed to partake in the collab.
AI Art : Obviously none
Photography : I'm pretty sure this does not break any rules, the collab was divided into 10 slides. One slide by solarfiction was just a series of images of drawings made on paper specifically made by solarfiction himself.
Third Party Assets : None
Advertisements : None
Multiple Image Variants : Did everything correct there
Age Guidelines : Artworks had nothing to do with NSFW, so the majority in this section is off the list here. No rules broken here.
Content Ratings : T was fine. Couple of wacky jokes were added that raised it from E, but regardless it was not M or A-rated material.
M-I Content Ratings : No rules were broken.
Hate / Bullying : No races were made fun of, no slurs, etc.
So, yeah.. Personally I don't think it broke any of the rules, some people who saw it can of course debate me on it, but it was a huge birthday gift and I'm a bit sad that it went to waste.
I don't wanna make this a big deal either, for ours sake, if it's not welcome on Newgrounds somehow, that's fine! I can upload it somewhere else, just a tad confused. :)