The Internet Archive (archive.org) hosts several comprehensive collections for downloading
Ben 10 - All Episodes (2005–2008) Complete Series Download | Archive.org
franchise. While the platform is a digital library for preserving media, it is important to note that many of these files are uploaded by third parties and may be subject to copyright removals or access restrictions. Available Ben 10 Series on Archive.org
Omniverse Coverage: Provides a separate, complete set for Ben 10: Omniverse spanning Seasons 1 through 8.