First off, let me just say that if this has come up before I'm sorry I just didn't find it since I tend to get turned off of a thread once it goes firestorm. Secondly, please know that I am lucky in that my players typically do not look for ways to abuse the system. In fact, the reason I'm finally looking at something for overcasting/oversummoning is for a magical threat, prime runner reoccuring style npc. It isn't my goal to just 1 shot any party member because of something like this, but I do wish to cause them to cringe (or possibly even open the eyes of the newer SR players to the magical 'oh shit' button). That beind said, here is a houserule idea I had to deal with overcasting and I'd like to get some feedback:
1. When overcasting a spell, you do not divide the force by 2 when calculating drain. For example, a force 10 stunbolt would to 9 (10-1) physical drain, and not 4 (5-1) physical. This does not affect normal casting, only overcasting.
The way I see it, that would encourage more split dicepool casting of normal spells most of the time, but still leave mages that 'I need to put all I've got into this' option when needed. I would love to get feedback on this.
Now, on a conceptual level, there is only 1 real problem I see right now: How do you approach oversummoning? That got me thinking of the following:
2. The easiest thing is to double the drain damage value for spirits when oversummoning (hits x4 instead of x2). That number might seem absurd, but then I don't see an average of 12 physical damage for a force 9 spirit as too out of line (3 successes x4), where 6p average just isn't high enough. I could however see going with something like +1 multiplier (x3 instead of x2) instead, which would still be around 9 Physical average on that force 9 spirit. This is the area I'm most stumped on, so I'd love input. The general idea though is that overcasting not only makes the drain physical, but it increases it by a significant magnitude.
I numbered the points for easy reference, and am very interested to hear what people say (and hopefully we can keep the asbestos lining on the thread walls to get some good ideas).