Me either, but it would fit in (if D&D used normal laws of physics).
Oh the HR wouldn't be to bad I suppose. Just state that any spell that effects one member of a grapple effects them all. Sometimes it would be useful sometimes not.
Useful - a mob tries to hang Malaroc three of them grab the man and start to carry him towards the gallows. With one spell Jareth knocks them all out and Malaroc has enough HP to survive.
Un-useful - the same mob tries to hang an NPC who you know won't take the shock, so you have to find another way to stop them.
In D&D you can explain away anything, perhaps the spell is more centered the remaining energy doesn't effect the other person in the grapple but they do feel a slight tingle. Or it causes a release as soon as the creature is hurt and wails about.
All that is not what worries me as it will be limited and used limitedly, What concerns me is the effect on Jareth. Here I have a good way to write off a PC whose player is no longer about and have some character development happen. But do I want this kind of development?
Jareth has had a lot effect him in a very short week (maybe only what 5 days since being tied up and accused of treason) and I'm not so sure more is needed. Had this been any other player's character I wouldn't be thinking this and would have HRed and played through.
Right then. I'm not going to because it wouldn't be fair unless I
could do it for everyone. When a change would really only effect one player than that change is no good. I'm sure the next battle will give me an opportunity (should have never rolled for those first to attacks but how did I know they would both miss only need a 4 or better to hit

).
"I'll get you yet Cedric. And your little crow too. ehhehehehehe!"
HM