Circle Casting

     I'm working on a thing about hags. A hag is basically a witch, right? Witches famously cast spells as a group, and they're not the only ones, but the rules for casting spells with others, at least in 3.5, are distinctly lacking. It's also possible that I haven't seen them, but who has time to look through every splatbook for the one mechanic I want when I could instead just make one? I know that the Monster Manual has a section on hag coveys (is coven a copywritten word?), but I find the definition much too specific and also just boring. It adds spells they can cast and technically ups the save DCs, but ultimately it means that cooperative casting has a very definite point at which it is no longer effective, which feels wrong to me.

    Here's my suggestion for how to circle cast: the requirements are that there are two or more participants, all participants know the spell being cast, are in physical contact, and all pass a -20% spellcraft check (call it a -4 in a d20 system). If the spellcraft check is failed by any member the spell as a whole fails and all members lose the spell slot. If the group as a whole has more degrees of failure than there are participants, something magically horrible happens (read: 40k perils of the warp). On a success all members still lose the spell slot, but the spell is cast. The spell requires 10 minutes per spell level to cast, reduced by 5 minutes per total degree of success on the spellcraft check. Caster level and spell save DCs are taken from the leader of the circle. Choose from one of these benefits:

• Add one die to the dice pool per caster in the circle, e.g. a three person circle led by a fifth level spellcaster all casting fireball increase the damage from 5d6 to 8d6.
• The effective caster level for the spell increases by one for every two casters (rounded down) in the circle.
• The spell save DC of the spell increases by one for every two casters (rounded down) in the circle.