Here is another spell from GURPS Magic I've chosen to modify for my DF game.
Windstorm has a few problems.
- a ST roll. This is not terribly effective in the first place, and outside of human scale it's basically useless. I like ST vs. ST rolls, because they work fine in play. Straight rolls against a stat that is routinely well above the bell curve of 3d? Not so great.
It's odd that you either get blown over, or you're fine.
- Odd penalties. -5 to DX skills is okay, but -10 per hex to "ranged attacks" - so, lasers, Lightning spells, etc. are at -10? They're ranged attacks. -10 is also steep. A Scout with Bow-20 standing adjacent to a target shoots at a 10 skill. Maybe a 5, if these stack (-5 to DX-based Bow, -10 per yard.) Plus distance penalties, presumably? It doesn't replace them.
Wall of Wind has a similar effect, but it's -3 DX and 2d knockback. Shape Air can do up to 5d of knockback damage at the 10-point level. Neither of those is terribly effective - 5d is 17.5, which knocks back all of a ST 19 person 1 yard, or a ST 7 guy two yards. Not much for 10 points, even if it's on for a minute. Air Jet does 2d/energy of knockback (also weak, but damages swarms and vaporous beings.)
- strength for moving objects varies by size, but nothing else does.
- Inconsistent effects between the two strengths.
We've played it as written and it's mostly been okay, but it really could smoother mechanics.
Here is what we'll try in play.
As written, except:
- All DX-based skills are at -5 within a windstorm.
- Thrown weapons, physical missile spells (such as Stone Missile or Fireball), and low-tech missiles are at -10 if they pass through any amount of Windstorm. Bullets and similar missiles are at -2. Energy missiles and energy-like spells (Lightning and Sunbolt, for example) are unaffected.
- +1 Movement cost per yard of wind crossed, and each yard moved (or each facing change made) requires a DX roll to remain standing.
- Blows small objects up to approximately 5 pounds.
At the tornado level, as above plus:
- Visibility is limited; Vision rolls are -10 per yard.
- Thrown weapons, physical missile spells (such as Stone Missile or Fireball), and low-tech missiles cannot penetrate the storm (or fly off course, per Scatter, if cast from within it). Bullets and similar missiles are at -10. Energy missiles and energy-like spells (Lightning and Sunbolt, for example) are unaffected. All of them require some way of spotting the target!
- +1 Movement cost per yard of wind crossed, and each yard moved (or each facing change made) requires a DX-3 roll to remain standing.
- Blows small objects up to approximately 30 pounds.
I'm not sure how this will play out, but that's the version I expect to try in play. I may tweak any or all of the above aspects, but I like the movement/falling rules.
This has spill-on affects for Spark Storm (as written, but the Windstorm portion works as above) and Body of Wind (the knockdown and DX effects are as above).
Next up might be Air Vortex, which is really very strangely worded. I may have to go back to its original form, Carpet of Yimsha, in GURPS Conan, to see how it's all written in the first place. It comes off as a weird attack spell, but it's really "Mass Body of Air plus we all move together."