While not every spellcaster who could cast the spell was aware of it, the Minor Globe of Invulnerability that could be cast via the spell Greater Shadow Conjuration actually filled a significant role in d4 caster balance. Right now, Balagarn's Iron Horn is an extremely powerful and reliable kd spell against non-str builds. My understanding of the reasoning behind this is that it's to serve as a check against dex builds that would otherwise be incredible hard to counteract in weapon combat in the wake of the change to Word of Faith (since the semi-reliable blind formerly made massive ac from dex easy to deal with via flat-footing).
However, unlike dex melee build most d4 casters including EMA builds are generally dead if they get hit by Balagarn's Iron Horn by someone who knows how to capitalize on the opportunity window. This turns caster fights into a game of rocket tag where the first person who can breach the other's mantle and get a hardcast Balg off on their opponent sets them up for a long chain of guranteed cc (hellball and timestop already also forcing them to stay still) that is generally going to be lethal for a d4 hitdie caster.
The reasoning for why I feel like this is a balanced suggestion is essentially that Greater Shadow Conjuration isn't a very good scroll. It's CL 11 which means it takes roughly six seconds to cast and will last for 66 seconds making it a massive loss of action economy for someone spamming it via disposable. Meanwhile, being unique to the GSC version of Minor Globe of Invulnerability also means that the spell cannot be extended and so will last at most three minutes which is fairly short even for the tempo of fights on Arelith and so there will likely be a need to re-appy the buff at least once over the course of combat.
If this seems imbalanced for some reason because there are a few casting classes that don't have d4 hitdie but which receive Greater Shadow Conjuration then the nature of this suggestion changes to suggesting a new spell with the same general dynamics of an unbreachable and unextendable Minor Globe of Invulnerability that is exclusive to d4 caster spell lists to resolve the balance issues around Balagarn's Iron Horn that I've discussed. The reason I don't feel this is an issue with Balagarn's Iron Horn itself is that I feel the spell does still serve an important role in the overall server balance and I similarly feel that casters with more hp can at least soak up enough damage that alongside other tools like -pray they will likely be able to survive getting hit by Balgs even if they are in a worse position for having been struck by it.