When Rhineheart comes at you in the final level, start firing your missile gun immediately. During some periods he will shoot ground level blood lines. Just dodge them. Other times he will shoot full circle blood waves. Jump those. If he gets close enough to you, he will pick you up and start punching to severely drain your life. When he gets low on health he will run to the altar to recharge. If he recharges you must repeat the process all over until he is dead. Face the altar when he picks up the book with his powers to recharge. Kick Sam towards the book, unhooking Rhineheart from recharging. Repeat the missile launching and dodging the blood lines and blood waves. Remember to stay away from him. Repeat kicking Sam towards the book. When he is low enough on health he will basically slowly walk back to the altar. This should give you enough time to finish him off.