The quests where not implemented in multiplayer, only singleplayer. The PS1 port is based on the single player mode, but has hot seat 2 player support, this was still actually the single player mode as there is no networking and the players can't be on different levels, which is why quests work there.

I think the real question is what version are you playing now? The GOG version is still just the 1.09 release from 2001 so has the same limitation. Though the DevilutionX port does allow you to play all quests in multiplayer since we implemented the missing network synchronization for guests and custom dungeons.

Ahhh I see! I must have been only playing multiplayer before. I remember the PS1 version of Diablo, playing 2 player you were both locked to the same screen.

I have been playing the GOG standard Diablo release lately, on single player. I just tested making a multiplayer character, and indeed had the options for Normal/Nightmare/Hell, and the shortcuts were open, like I remember. In hindsight I should have just checked multiplayer, but the version I remember playing was back in 1997, so I thought maybe I just forgot them or misremembered something. Thanks for your comment.

Im a bit old to this and yet.
Sony PS version is kinda riffer obviously.
And Diablo v.1.0 is differ to Diablo: Hellfire 1.09+1.01.

Many... or maybe even most - games in v.1.x with lowest release-hotfix patch was much differ from latest revisions. Especially games with Exp/AddOn/DLC's. Some features lost. Its not so rare.
Warcraft 2 ToD v.1.x looks a bit harder and one video sequences changed with addon+latest DOS patch to worse version (unarmed King's guards that strange).


And as already said previously - MP mode have differ balance and features. With some limitations. Person above answer directly to the topic subject. But there is a bit more differences than just some quests exclusions. Some difficulty/balance changes and some items not available on MP mode. Same info provided here by same person, so thanks to him to answering this many times here and this thread.

And still it can be good idea (if you hard fan) to find earliest Diablo 1.0 North America CD edition and earliest (1st/2nd?) patch. And play as it was back then. Or play Sony PlayStation version. And ofc latest GOG release of Diablo: Hellfire.

What i dont see a point to play is Diablo 1.09 executable while hellfire.exe is same and more. Diablo without Hellfire is SonyPS version (a bit older than 1.09 but still).

And as answered above: for MP mode with full SP content - more modern fanmade ways to play. Again, some quests AND ITEMS not available normally in MP in Diablo 1. It is one of important improvements of DevulitionX. I dont see balance reasons to keep it off since this game is plot singleplayer-like cooperative game.

Hellfire also replace one quest as i remember. And have hiddend not finished some else and they cannot be modified to ADD to the game (unlike Monk class). Only possibly is replacing another quest. Not such important but improvment too.

Hellfire is based on 1.04 with a few bugfixes, but also many new bugs. It never recived the 1.05 - 1.09 fixes.

PS1 version is also based on 1.04 i belive, in singleplayer mode (also with playing 2 heros) but also has many unique bug fixes and replaces the the knights on the last level with skeletons. Like hellfire it never recived an update with other fixes.

i have both versions myself. the playstation version is an adapted single player version of the game i believe. it have certain multiplayer only stuff like resurrection and heal other. friendly fire was a serious problem. i played single player on pc back in the 90s and it was only later that i tried multiplayer. te butcher does not always appear in single player. only quests that always appear is the curse of king leoric, archbishon lazarus and diablo. other quests is always random. multiplayer have the butcher as another fixed quest with no random ones.

leoric is also random in single player