From Halopedia, the Halo wiki
Mythica.org was a file hosting website that was dedicated to hosting user-created movies to do with games, mainly Halo 2.
It hosted files directly submitted by users (useruploads.mythica.org), and also did mirroring for other websites like HBO (www.mythica.org, www2.mythica.org, files.mythica.org). The first three have all but gone, but files.mythica.org still serves because of "Louis Wu" (HBO operator) now paying for bandwidth on that server.
Many videos have been lost from the downfall of files from www.mythica.org/halo/hbo/*, but you can still retrieve them. Copy the path after www.mythica.org/halo/hbo/ and paste it onto mythicafiles.bungie.org/halo/hbo/. All the files that were mirrored on Mythica are on the mythicaFiles.Bungie.org server.