"Call For Backup Opponent's property too well protected? Call For Backup using a Burner to get a second strike at success.
Call For Backup will provide a boost of attack from a Top Mafia member to help you defeat your opponent and rob their properties.
Increasing your Robbing Mastery level will up the maximum number of Burners you can possess."
It is a consumable and can be asked for periodically. Once asked it will publish on the newsfeed and your friends can help. They will receive one for helping as well. There is a limit on how many one can have at a given time based on robbing level.
Burner can be used as a cumulative effect to rob a certain property, provided you havn't succeeded in robbing it. For example, if you don't succeed in your first rob and also on your second rob using your first burner that adds 300+ atk bonus, the second burner will provide additional bonus up to 1000+ bonus. This cumulative effect adds up for the third, fourth burner and so on.