If you want to legally enjoy the quality, you should subscribe to Max (formerly HBO Max) and download the special through their official app for offline viewing. However, offline downloads from streaming apps are DRM-protected and cannot be played outside the app. Third-party release groups strip this DRM — a legally gray area in many jurisdictions.
Frank Welker (Scooby-Doo / Fred), Matthew Lillard (Shaggy), Mindy Cohn (Velma), Grey DeLisle (Daphne) Scooby-Doo.Haunted.Holidays.2012.MAX.WEB-DL.108...
– but that’s actually a TV special (22 minutes), not a full-length movie. It premiered on Cartoon Network in November 2012. If you want to legally enjoy the quality,
(or a similar truncated version).