Go get cursed. When you do, your hp will be below 100, so power within will drain your hp at 1 hp per second. That's the same average healing rate as the sanctus. This means you can freely use power within without fear of running out of hp. Get your hp into red tearstone range, activate power within, toss on the sanctus, and spam boss battles with sorcery. This build wrecks even ng+4 four kings easily.
