When you fight luther on the beach, order your comrade to hide behind the boat in the far back. If he is out there he will just be wasting all your bottles and making it harder for you to get a good shot at Luther. He will be better off there so when Luther orders his men to attack all you have to do is run back behind the boat and order your warrior to help you bust their heads open. If he is on the beach with you it just means it is harder for you to run and it will make it harder for bottles to pop back up. Also when the 'throw knife' option is open, take it don't bother
bringing down Luther's life more, it's pointless. This option should spring up when he is at about half health and you have a knife so stay alert.