Do players have any choice in your variant? It looks like you could just roll all the yellow and red dice at the same time and reroll the feet until they came up as blasts or brains, then tally the result.
see if you can rack up 13 brains (or any number of brains that you choose) before you reach a certain number of shotgun blasts that you set before the game starts (shotgun blasts must always be lower than the number of brains you need to get to win). for instance.. say you go to 13 brains. You can see if you will rack up the 13 brains before you get 7 (or whatever number you choose) shotgun blasts. You play as normal just you keep track of how many shotgun blasts you get so you will record both your brain score and shotgun blast score. You do not lose your shotgun blast score as you do your brain score when you rack up 3 shotgun blasts. You will keep track of all shotgun blasts that you recieve.
Example play:
Object:Getting 13 brains before reaching 8 shotgun blasts.
The game play: You play as normal. Shake up the dice and pick 3 dice to roll. After rolling the 3 dice, you count the brains you have plus shotgun blasts and set them aside. Any feet you get need to be rerolled with other dice in the cup to make 3 dice you roll. When youve reached 3 shotgun blasts you will lose your current brain score you racked up for that round. The dice currently being used and the ones set aside now go back in the cup but be sure to keep track of your shotgun blasts. This score never goes away and is always scored when you roll them. Play again as normal until youve either racked up 13 brains or 8 shotgun blasts.
When you get 13 brains before being shot 8 times you win. If you get shot 8 times before getting 13 brains, you lose!