House Rule: Nerfing the Concussion Spell

The Concussion spell in GURPS Magic and DFRPG: Spells is too good.  It's basically a missile spell that inflicts 1d of crushing explosive damage for each 2 FP you put into it, which is nothing special.  But the side effect is -- everyone within 10 yards must roll vs. HT-3 or be stunned, and then recovering from that stun takes a roll against HT-3.  And there are some bonuses to resist if you have hearing protection, which is pretty rare in most settings that use magic.

So, the list of problems:

• The 10 yard range of the stunning effect is both too large, and too fixed.  It should be smaller, and vary with the amount of energy put into the spell.
• The -3 to the initial resistance makes it very difficult to resist, and this is also fixed rather than varying with the amount of energy put into the spell or the range to the target.
• The -3 to recover form the stun makes it very difficult to recover, and also requires tracking a new flavor of stun.  (GURPS Game Aid for Foundry VTT, for example, has a nice stun counter, but it doesn't have a second stun counter just for Concussion.)

And my list of fixes:

• Leave most of the spell alone.  Casting cost, prerequisites, and type and amount of damage done are all fine.
• The stunning side effect's radius should be the dice of damage in the spell, with a maximum of 10 hexes.  So a 1d Concussion only hits one hex, a 3d concussion hits a 3-hex radius, which means the target hex plus every hex within 2 hexes of it.  And the biggest possible blast radius for a Magery 6 caster with a huge power item who can cast an 18d Concussion is capped at 10 hexes.  (It's a forced circular area, unless the GM rules it is constrained by terrain features that would block sound waves; the caster can't manipulate it into funny shapes to hit more enemies and fewer friends.  It's a Missile spell with a blast radius, not an Area spell.)
• The HT penalty on the initial stun roll should be the number of dice of damage in the spell, capped to the original -3.  So it's HT-1 to resist a 1d Concussion, HT-2 to resist a 2d Concussion, and HT-3 to resist a 3d or larger Concussion.
• The stun should be a regular stun, so the recovery roll should be versus full HT, not a modified HT.

The net effect should be that it's still a good stunning spell, but if you want the original HT-3 effect you need to make it at least a 3d spell (so 6 FP), and if you want the original radius 10 you need to make it at least a 10d spell (so 20 FP).

I think it's still a pretty good spell even with these changes, just not quite as broken.  But I'll give any players who disagree a chance to put their points in a different spell, for a limited time.