It looks like the GOG version still has the mana cost bug which was introduced in Hellfire patch v1.01

It causes all spells to be reduced to minimum mana cost straight away, rather than the mana cost reducing as new books are read.

To reproduce:

Create a new lvl 1 sorcerer. Look in the spellbook. You should see firebolt at spell level 2, doing 7-16 dmg:

When the bug is present, the spell only costs 3 mana (min possible for firebolt) - this happens in the gog version of hellfire, or original Hellfire with the v1.01 patch applied.

If the bug is absent, the spell will cost 6 mana (normal for spell lvl 2) - this is the case in the gog version of diablo without hellfire, or pre-gog Hellfire v 1.00

This bug pretty game-breaking for the sorcerer, since their main way of character advancing is reading new spellbooks and they are (even more) overpowered with this bug.

Ha! Hadn't noticed the footsteps.

I'm _hoping_ it's going to be possible to fix in Hellfire, since Blizzard are still around and they've got the source code, which I guess won't always be the case with the games gog has picked up from out-of-business developers.

Fingers crossed, anyway.

let us get one thing straight: hellfire was not made by blizzard. it was made by sierra which was shut down once vivendi and activision was merged. as a result: they can likely not give gog the source code, only the publishing rights.

Also, Diablo was last patched more than 15 years ago. I would not be surprised to learn that in that time, Blizzard has lost the ability to build Diablo, whether by losing the source code (hard drives die, backups get overwritten, etc.), the tools required to build it, or both.

If I am correct, then the footstep sounds were removed from the game in the hellfire expansion. (so it is not a bug)
If you check it, in the normal game without hellfire there are footstep sounds.