It's possible to play multiplayer with Belzebub-like HD. There's a mod named Tschernobog (from the same author). It's focused on multiplayer (coop via LAN / Hamachi).
Video: https://www.youtube.com/watch?v=mNKfgN-0UVQ
Edit: forgot to post a download link: http://diablo1.ovh.org/hd/?download (same page as Belzebub)
Video: https://www.youtube.com/watch?v=mNKfgN-0UVQ
Edit: forgot to post a download link: http://diablo1.ovh.org/hd/?download (same page as Belzebub)