User blog comment:AwesomeGamer/Smashpedia Plagiarism?/@comment-7697305-20140426033126

As I understand it, the reason for that is that SmashWiki forked with this site some time back in 2010 or so due to dissatisfaction with Wikia. As part of this process, the people who were forking took copies of most of the pages here over to the new site (which they were within their rights to do due to most content on Wikia being licensed under the CC-BY-SA license). The histories of pages ported in this way were preserved, too: compare the early parts of this with this and notice how they are pretty much identical.

So, it's not exactly plagiarized so much as the wikis haven't "de-cloned" yet.