Fanfic, including derivatives, such as @RockmanX 's, are allowed to be posted in the Hobby topic here and hosted on DD and Ink under the fair usage laws, as long as they do not break Choice Script and Hosted Games rules.
Personally, I feel, a person should get permission from the origins author(s) before pushing fanfic into the wild.
So far, I have drawn the line between stuff I have published and stuff I have not published, but each author’s wishes (in my opinion) should be the controlling authority.
As a rule, I will not also read or even glimpse any fanworks based on my writing. More on this below.
Regardless, the following should be of interest to anyone writing fan-works:
and one of the most important resources (thank you @rinari, we miss you here):
https://fanlore.org/wiki/Professional_Author_Fanfic_Policies
The attitudes of professional writers and creators of source texts to fandom and fanworks are as varied as their understanding of copyright and Fair Use. Some are vehemently opposed to fanworks based on their texts, and some are actively supportive. Still others are fine with fanworks but believe that reading or seeing them constitutes a threat.
The lists in that article are not exhaustive, but do attempt to list the publicly stated positions of novelists and other writers (including television and radio producers) who have earned fannish attention.
The reason I will not read fanfic based on my writing, or even discuss it, is because I do not want it to influence me, subconscious or conscious. I want my storyverse to originate wholly from what I write, especially if it is an ongoing storyverse.
In RockmanX 's case, I hope he went to the original authors and listened to what they had to say, because that is what I would wish he would do if using my writing for his fanfic.