This spell has an interesting history.
Originally, it was Carpet of Yimsha, in GURPS Conan.
It's a GURPS conversion of the transport spell used by the wizards in The People of the Black Circle:
"Down the mountain-slopes, like a whorl or shining dust blown before the wind, a crimson, conoid cloud came dancing. [. . . ] The crimson cloud balanced like a spinning top for an instant, whirling in a dazzling sheen on its point. Then without warning it was gone, vanishing as a bubble vanishes when burst. There on the ledge stood four men."
- Robert E. Howard, "People of the Black Circle" (quoted from The Bloody Crown of Conan)
Those wizards use it to whisk away folks with them when they go, too. They take (of course) the woman of the piece, so Conan can go and rescue her. It's not clear how they take her (grab her, different spell, same spell) but they do and whisk her off. Conan sticks around, and it's possible he's staying because he resists the spell or because they don't want him at all.
Either way, in its original form, the spell is mainly transport. In the GURPS version, it's the same, although frustratingly it seems like you can't resist it.
"This spell allows a caster to fly all persons in the area of effect in the form of a giant, swirling conical crimson cloud. [. . . ]. The caster can choose which persons to pick up, and which to leave behind."
The other particulars are similar - Move 10, casting cost and time, etc. It says the affected subjects are "insubstantial" and can't cast spells, but cannot penetrate solid objects. It never says who directs this - the spell in the story is clearly directed as a unit, which probably means the caster. In GURPS Conan and later GURPS Magic, it's really not clear, especially if the caster isn't in it. If the caster can move it, it's an offensive spell and a transport spell. If the subjects can move it, you need to figure out who and it's an odd transport spell useful for when it's okay to lose everything but 6 pounds of clothing,
Air Vortex turns this, basically, into Mass Body of Air that can be resisted by DX or HT. Why DX? That's not clear. Body of Air is resisted by HT.
It changes the cost (8, 3) and prereqs (from Body of Air and Flight to Magery 2 plus Body of Air and Windstorm.
I figure I have three ways to go with this:
- turn it back into Carpet of Yimsha as much as possible.
- turn it into a mass transport spell.
- turn it into Mass Body of Air.
I like the idea of a mass transport spell. The cost (8, 4 in the original, 8, 3 in Magic) and movement is pretty cool. But that's not really fitting the air theme - if you want Mass Flight, it's better if it's scaled to work more like that. I'll leave that aside - my DF game doesn't really need Mass Flight.
Mass Body of Air is easiest, but it's not really very useful. It's actually more useful for offense (disarms your foes) than defense (we lose our gear) or utility (we can move together, and lose our gear.)
But perhaps just a utility version of the original spell would do - no as restricted as Body of Air, but a lot more focused.
Turns the caster and any willing (or unconscious, incapacitated, or helpless) subjects in the area into a vaporous cloud with the Body of Air meta-trait (p. B262). Any equipment carried, up to the caster's skill with the spell in pounds, also transforms with the subjects, but lose any magic powers they might have had while in this form. The cloud is the same size as the original casting area, but can squeeze into smaller spaces like other vapors. The cloud moves as one unit, as the caster wills, with Air Move equal to the 2 x the caster's Basic Move.
This is also a Movement spell.
Duration: 10 seconds.
Cost: 8 to cast, 3 to maintain.
Time to Cast: 2 seconds.
Prerequisites: Magery 2, Body of Air, and Windstorm or Body of Air and Flight.
I feel like that's a useful spell, but isn't an attack spell. I like tying what converts with you to the caster's skill one-to-one as BL, too - physical strength shouldn't matter, magical skill should. I may need to do that with Body of Air and Teleport (assuming I use that again). We'll see.
(PS - That story is where the spell Evisceration is from, too.)