So for 20 years Diablo in Nightmare, Hell, Uber Tristram and Dclone have a bug which makes them pathetically easy. I don’t see it mentioned much.
When standing very close to any variation of Diablo besides Normal Diablo, his most dangerous attack the lightning hose is released further from Diablo than it should be. This causes it to do zero damage if your character is standing close to him. I also think that this bugged version of the attack does less damage than intended even if it does hit. In fact I think all of his attacks may be bugged to do less damage. He really is a wimp.
Again in Normal difficulty he is fine.
Recently I watched a great few streams of MrLlamaSC beating the game with a Barbarian that used punches to beat normal through hell difficulty. If you watch this run you will notice how pathetic Diablo in Nightmare and Hell is. He didn’t even have to go back to town to heal because of how pathetically weak Diablo is in Nightmare and Hell. It took a while to kill him with punches but it didn’t matter.
For gods sakes just fix this. The game is called Diablo and the main antagonist has been bugged in Nightmare and Hell for 20 years. I am amazed that this has never been fixed. It should have been fixed within a few days of release. I have played on and off since the day of release and I can confirm this has existed from the very beginning.