The FAQ has a pretty good summary of managing the multiboss issue. Here it is: Q. If I am fighting a pack of bosses and I remove the last HP from multiple bosses what happens? A. First remove all bosses with no remaining HP dice from the board. If the attack would remove all bosses from the board leave the most North then Western boss on the board. Perform a number of reactions equal to the HP die that were broken (-1 if all were broken as the last die does not trigger a reaction). The reactions are performed by the surviving boss/bosses. Only bosses directly damaged by the attack will focus target the die breaker, all others will attack using thier normal targeting rules. Perform all steps that you can on each stage car and skip any that you can't.