Full Diablo + Hellfire Data Files download.
Previously, the version I uploaded did not contain Hellfire, nor the correct .ini file to make it operate. I've reuploaded it to the mega-post with the full data and decided to share, seeing as no one else has posted a link to the full download.
Hope you enjoy it!
EDIT: Diablo files have been reuploaded to mediafire, please use the same password as Sonic Mania, which is "Alpaca"