Try this by iKilledAppl3

//FrontBoard stuff
//Add this because we need it
//This is the way to reboot, power off, and respring using Apple's FrontBoard classes.
@interface FBSystemService : NSObject
+ (id)sharedInstance;
- (void)exitAndRelaunch:(BOOL)relaunch;
 - (void)shutdownAndReboot:(BOOL)arg1;
 -(void)shutdownWithOptions:(unsigned long long)arg1;
@end
//These are example classes
//Not actual methods
%hook classMethod
-(void)powerDown {
    //This is an actual method :P
    //This is to shutdown the device
     [[%c(FBSystemService) sharedInstance] shutdownWithOptions:nil];
        }];
}

-(void)reboot {
    //reboot the device
  [[%c(FBSystemService) sharedInstance] shutdownAndReboot:YES];
}


-(void)respring {
        //respring the device
      [[%c(FBSystemService) sharedInstance] exitAndRelaunch:YES];
}