if you create a mod with it, sure, otherwise such a thing definitely won't go into devilutionx as it's gamechanging

Is that some sort of cheat command, I'm not intimately familiar with d2. If so there is a debug cheat for that already.

It's a commnand added in patch 1.09 that simulates the presence of multiple players in your game.

Diablo 2 increased monster values (Def, AR, Damage, XP rewarded) and affected the amount of item drops. The precise effects and possible amount of players changed with different patches: https://diablo2.diablowiki.net/Player_Settings
It doesn't require any form of enabling debug or cheats, you can activate it at any time in single player and in multiplayer outside of battle.net/D2 game servers.

Ok, well Diablo doesn't have a scaling mechanic like that, so faking the number of active players wouldn't have an effect. We don't really plan to add difficulty scaling to DevilutionX either, but there has been some attempt at modding it into the game:

https://github.com/diasurgical/devilutionX/pull/1413

"If you can reproduce, the bug you should report it. And while at hat you can always create another issue with proposal! You never know someone might start working on it!"

I think the bug might be caused by an armor or weapon breaking due to durability = 0, thus forcing the game to load a different set of animations but somehow failing to communicate that to the other clients?

You should report it on Github

Do most people on these forums play Devilutionx, or just Diablo Classic? I'd rather devote time to building characters like a LAW or LAR (Low Armor Warrior/Rogue) for whichever one has the more active player base.

Save games are interchangeable and gameplay is the same except for the bugfixes

How? I copied my multi0.sv file from my Diablo folder into my Devilutionx folder and it's not showing that character on Devilutionx.

saves are located in %appdata%/diasurgical/devilution/ by default

May I ask what combination of settings results in optimal integer scaling to 1440p from the original 480p resolution (scaling, fit to screen, etc.)? I've consulted the GitHub manual, but it's a bit unclear to me.

Your resolution is 2560 x 1440, right?
The original game was 640 x 480.
So a x3 scaling would give 1920 x 1440.

This would seem perfect for your 1440p resolution as you fill the full vertical resolution, and maintain the 4:3 aspect ratio with pillarboxing, but DevilutionX will also allow you to play widescreen, so should then fill the areas on either side.

Ok, thanks! But what's the correct setup as far as the resolution/scaling/Fit to Screen settings go?

I can't be sure, as I don't have a 1440p monitor to test on, but I would assume it is something like the below:

[Graphics]
Width=640
Height=480
Fullscreen=1
Upscale=1
Fit to Screen=1
Scaling Quality=0
Integer Scaling=1

Basically, use the original game resolution for the internal resolution, enable upscaling so that it scales to your monitor screen, and fullscreen, then use integer scaling. I've set scaling quality to 0 as you should be getting pixel perfect scaling so the nearest pixel will be the matching pixel anyway, and I've set the fit to screen option on so that you get the full widescreen rather than a pillarboxed screen.