This should stop him cold. They can pick up uncontrolled groups with no competition by spending 5MB for a privileged attack. This can be used against any group. Holding a member of the player's family until he promises to give his most powerful groups to you and assist you in any way possible.
Tranquilizer darts are a good bet here.
Best for their restructuring capability. The combination of the Mafia and the Bermuda Triangle capturing something and reorganizing it to another area can be devastating. But not, obviously, as devasting as a shotgun blast to the shoulder. Whoever lives by the weird, dies by the weird. Or at least injured.