I downloaded the Offline Installer. (Don't want to use GOG app!) I try to run the B.Net Updater and I get "This does not need to be run." and when I try to play on B.net I have to update.

How do I fix?!

This happens because it's unable to look up what the "latest vesion" is, this is probably because the network is down.

For multiplayer I would recommend using DeviutionX, it simplifies the process, bring new QoL features and fixes many bugs:

https://github.com/diasurgical/devilutionX#readme
(I'm a developer on the project)

Alternatively you could also download the patch 1.09 manually and most likely update that way, but I'd also recommend DevilutionX.

The GOG installation gives you 1.09 from the start, so there should be no pending updates.

Diablo 1 GoG version runs on 1.09b (latest official patch) no need for updates.

"No need to update.."

That would be great if that were the case but it's not...

It's not that we do not believe that you are seeing this message, we are telling you that the message it self is erroneous. This is what happens when it fails to connect to battelnet. There has been no updates to the game for over 20 years. The GOG release is the same version 1.09 that came out in 2001. But the Battel.net service provided by GOG appears to be having issues which is why you are getting this message and why we are suggesting alternatives for how to play multiplayer.

Thanks, that makes more sense. Because just saying that I don't need it when the game says I need it didn't make any sense.

So what you are saying is I need to connect to a different Diablo 1 server because GoG's Diablo 1 server is not working or there isn't one and this doesn't connect to Blizzard Battle.net Servers; which was my initial impression.

You could have just said "The Battle.net Multiplayer functionality doesn't work."

Well that is what I said in my very first line of the first response:

> This happens because it's unable to look up what the "latest vesion" is, this is probably because the network is down.

I guess maybe you took "network" to mean something different then the "GOG Battle.net".

Battle.net multiplayer functionality did work at one point after the GOG release (though from what I've read, it was fairly sparsely populated), and Battle.net might yet work again if the relevant server is repaired, so it isn't really correct to say that it doesn't work at all. It is only broken now and for an indeterminate duration into the future.

bnet is dead and was dead even when it worked - it might've been fun 25 years ago but there are better ways to play online nowadays

I interpreted this comment from OP as saying that: I thought OP's characterization was excessively broad and pessimistic, as I read it to mean that he thought battle.net multiplayer was completely broken forever. I posted to point out that it once worked, with the same binary as OP uses now, and may yet work again, if the server is repaired.

Yeah, we won't know the future until it happens... or don't...

If you or Windows remove (or prohibited to read) entries for Bnet gateways game try to connect to old servers. Gog exe (all) detected as outdated.

If you try DX exe you get that message

If you manually start Updater (before try to go online), it overwrite Bnet Win REGEDIT entries as well as battlenet.sp file. And maybe even exe (although report it didnt do anything).

Anyway you need first reinstall the game even if at first it be temp offline server of Bnet. Now your version are downgraded. GOG Galaxy somehow possible to detect installed game as Galaxy build version, then verify installation (at least twice, first one redownload something). That also fix win registry.
Or look to info/script files (goggame_xxxxx) for correct registry. But still sp file most likely are downgraded.

Devuilition(X) authors say their mod need only diabdat.mpq (and hellfire mpq?), so that way can fix issues with 'cached' files from Bnet from game root or AppData folders.
Issue come with GOG releases and new Blizzard Global server. They are no back- or forward- compatible, and broke functionality for other (differ exe files). The wrong exe (or start old Updater) and you must reinstall game. Although two separate game folders and manullly edited Bnet gateways to list 5 servers (4+1 new) make possible to use old and new. Just careful with exe files (you need exe from 1.09b patch to connect to old servers, gog one are not equal to 1.09b). One miss click on exe and both installments need to be reinstalled.
________
Do not start the Updater.
.....

If install DevuilitionX right into GOG folder and run Updater after - get some files downgraded - connect to mod server overwrite it back, right? Like old Bnet do before Global server (which one are kinda broken in that and instead of overwrite files return errors). It is don't care about existed SP or any else "minor" files?