When did a little extra flavor hurt anything?
And, in one form or another, it's all from the original critter.
Okay, if we're going that route we might as well go the whole hog and include the bit about them appearing in lightning storms on the Prime Material Plane where they "feed and reproduce". I'm inclined to excise the bit about few high-level casters knowing the secret to summoning them as it seems too campaign-dependent.
We've got the following original material for the background info:
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2E AD&D Planescape Appendix III
The Quasiplane of Lightning is a wild and dangerous place, and the living embodiments of the realm are no different. If any of the quasielementals (or paraelementals, for that matter) could be said to lean a bit more toward chaos than pure neutrality. it’d have to be those of Lightning.
HABITAT/SOCIETY: Intelligent lightning quaielementals flock together in the constant storms of their home plane in a display that outsiders'd call a huge electrical conflagration. No one knows the dark of what happens during these gatherings. Some think it's for reproduction, while others say the quasielementals meet to exchange information.
Beyond these mysterious assemblies, the creatures seem to have no real organization. No lightning quasielemental ruler is known to exist, nor — does it appear — could one. The beings are truly alien, somewhat chaotic loners.
ECOLOGY: Virtually nothing is known or the life cycle of lightning quasielementals. Still, it’s clear that they’re the undisputed masters of their plane. Should a need for hierarchy arise (which it hardly ever does), the creatures known as shockers are almost always subservient to the quasielementals.
1E AD&D Monster Manual II
Creatures of this sort inhabit the Elemental Plane of Air and the Positive Material Plane. They are rare even in those places. During a great lightning storm on the Material Plane, large numbers of lightning quasi-elementals will sometimes gather. During such violent thunderstorms, the creatures feed and reproduce.
Lightning quasi-elementals have no known social organization. It is generally not possible to conjure quasi-elementals, although powerful magic-users have been known to do so.
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Boiling that down, how about:
Lightning quasi-elementals inhabit the Quasi-Elemental Plane of Lightning, which is formed from the junction of the Positive Energy Plane and the Elemental Plane of Air. They are the masters of this dangerous plane, being its most powerful inhabitants.
These living embodiments of lightning can be as wild and random as the constant storms of their native plane. Some sages claim they lean slightly towards Chaos rather than being the true Neutral of a "proper" elemental, but there is no proof of this.
Lightning quasi-elementals are loners, but do occasionally gather together in flocks to feed, reproduce and exchange information. These meetings occur in the hearts of the strongest lightning storms of their realm. Sometimes these storms are so powerful they tears interdimensional rifts to a lightning storm on the Prime Material Plane, allowing members of the flock to use their Arc ability to visit the Prime Material for as long as the rift lasts. They always return to the Plane of Lightning before the rift closes unless they are trapped by a
dimensional anchor spell or other misadventure.
Lightning quasi-elementals have no known leaders or apparent social organization among their own kind. Elemental creatures called shockers will nearly always submit to their orders, but lightning quasi-elemental very rarely ask them too.