The Dark of the Lady
...an introduction for the clueless written by Icewind
Not only does the Lady of Pain have the power to kill with a glance, she can create special Ethereal demiplanes called Mazes to hold those that cross her. Sages talk of the Communals, a faction who believed that everyone should share. Well, one day these cutters tried demanding that the Lady of Pain share her power, and they all disappeared - along with their faction headquarters - the next day. Seems like they're all sharing a Maze. Oh, and the Lady keeps the Power out of Sigil. With all those doors, every single god wants Sigil as their own. Sure, she lets their proxies in, but as soon as they cross her, it's to the Mazes they go, too. Still don't think she's powerful? What about Aoskar, the dead god of portals? She slew him and most of his followers (chant is, there's still a few left, and she lets them live out their miserable lives until they die).
The Lady's also one of the most mysterious beings in the Multiverse. No one knows the dark of her origin. Some say she was a Power, some claim she's Poseidon's daughter, some say she's a prisoner in the Cage, some say she's even a being from the Ordial, a plane said to link the Inner and Outer Planes (but no cutter's ever been there, so how do we know it even exists?), while others will tell a cutter that she used to be burgher of Plague-Mort, gate town to the Abyss. Some sods claim that she's the source of all pain in the Multiverse, that the Powers want to break open Sigil so that they can get to HER, not to the portals. They say that all pain in the Multiverse flows from a void in her chest. Far-fetched as it may sound, this theory does have some merit. About the only thing that these barmies, bubbers, and sages can agree on is that she's True Nuetral in alignment, but what else would you expect from someone who's spent eternity on the exact center of the Outlands.
Now, many bloods will tell you that magic loses power on the Outlands as you get closer to the Spire. One of the Guvners claims that maybe the Spire sucks in magic to bolster the Lady's strength (she IS fighting off every single Power in the Multiverse every second of every day, and believe me, that takes serious POWER). That idea's no better than the others, but no worse than a few.
Truth is no one knows who or what the Lady of Pain is, except that, well, she's the Lady of Pain. Even a stinking bubber can tell you that she's got power galore and that piking her off is probably the dumbest thing anyone can do.