Dresden Files: New York
Backlash and Fallout
Backlash affects the wizard; fallout affects the environment or other nearby targets. You get to choose how much backlash you absorb, with the rest going to the GM as fallout.
Backlash means that the spell energies run through the wizard, causing injury or other problems. This manifests as shifts of stress, which could require the taking of consequences in the usual way. You can choose to take the backlash as either physical or mental stress (but not split between both). Any uncontrolled power taken as backlash remains a part of the spell and does not reduce its effect.
Fallout means that the spell energies flow into the environment, causing unintended consequences. This can manifest in a number of different ways. The GM may place aspects on the environment or on targets that the wizard didn’t intend to hit (like his friends and innocent bystanders), or the GM may assign stress and consequences directly. The GM is encouraged to think of the worst applications of Murphy’s Law possible and enact them. Every shift of fallout reduces the effect of the spell.