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There is an abundance of fancruft on Wikipedia. Fancruft generally falls into two categories:
- Copyright violations: Stuff that's directly pulled from copyrighted material and is unoriginal to the point that it is a derivative work that cannot be released under the GFDL. 
- Fan analysis: Stuff that's pulled from copyrighted material, but created enough original fan analysis to the point that it is a derivative work which is unencyclopedic, but legal.
An example of this is the Back to the Future timeline. Is it an original work? If you say no, it is a copyright violations. If you say yes, then it is in violation of WP:SYNTH and should therefore be deleted.