So I am running a planescape campaign. My party just went into a color pool on the astral plane and got deposited in the outlands. They just got a magic carpet and I have a feeling they will try to use it to fly towards the spire and sigil. My question is at what ring do magic items such as a carpet of flying lose their magic? I cannot find the answer to this in any of my planescape books.
Manual of the Planes—the most recent supplement to describe this feature of the Outlands in much detail—describes spells, spell-like abilities, supernatural abilities, and even deities’ powers being nullified as you get close enough to the Spire. Conspicuously absent from that list are magic items. There is a statement that “Magic items produce spells or spell-like effects” in the core rules of the same edition of D&D, suggesting they’re maybe covered by the rules for those, but there are a couple of problems with this.
That statement is extremely obscure. It’s unlikely that the authors of Manual of the Planes had it in mind.
This statement is in the section on the saving throw DCs to resist magic items’ effects—they seem to be really talking about “active” magic items, or possibly those specific items that describe their effects as casting specific spells or spell-like abilities (in the relevant edition of D&D, that would have included all potions, scrolls, staffs, and wands). Illustrating this fact is that the save DC in question relies on “spell level,” which most magic items don’t have (but those that specifically cast spell effects do).
The nullification of spells and spell-like abilities happens by spell level (first 9th-level spells, then 8th-level, and so on as you get closer), and again, most magic items don’t really have any associated “spell level,” so it’s not super-clear when each should be nullified—if ever.
Anyway, while Manual of the Planes doesn’t really clearly state that magic items get nullified, the descriptions of the place make it pretty clear that they must at some point. For instance, On Hallowed Ground describes rare “godsmoots” in which deities travel to the Spire to meet in a location where none of them have magical power to threaten the others—that wouldn’t make any sense if they could just empower artifacts ahead of time and use those.
The problem is that, since Manual of the Planes neglects to mention what happens with items, but we’re pretty sure that they get nullified at some point, we’re left with this hole where we can’t really say where that is. Probably things should just follow the same trends as spells: the most powerful mortal-made magic items should be nullified in the widest ring, between 1,000 mi and 1,100 mi from the Spire, and less-powerful magic items should be nullified as you get closer (with every 100 mi being roughly worth a spell level in terms of how much the power gets limited). Deity-grade artifacts would be fine until 400 mi, but then even they would start getting nullified—but they follow the opposite progression, the more powerful the creator, the closer they can get to the Spire. Within 100 mi, no magic should work; at that point you’d be looking at nullification at least as good as antimagic field.
they will try […] to fly towards […] sigil.
They won’t reach it. The Spire is infinitely tall, and you cannot ever reach Sigil that way, even if you don’t need magic to do it. Likewise, those who leave Sigil by going over the edge never land on the surface of the Outlands below. The City of Doors can only be entered via one of those many doors.