If your bloodlust gauge is at least 1/4 full you can do a bloodlust power move that is very strong and you can kill many enemies with those moves so it's coming handy if you are in trouble with many enemies.
By presing the 2 button and with the heavy weapon mode you can aim body parts and shoot them. They fly of the body making the enemy weak and their are going to die after a bit while so it's very convenient.
To defeat Beliar, you should have guns, and grenades. The blades do not work on him. Use the Magic Eye to find Beliar's weak point and shoot it. When you run out of guns, shoot the grenades at him.
He must be defeated quickly, because if he powers up enough, you will lose. After Beliar is dead, go after Wulf. He will run around the room and attack you. Hit him as much as possible. After a few hits, Rayne will stop and say "That was for Mynce".
Wulf will tell her that she is pathetic and all, and the fight will continue. Repeatedly hit Wulf to win.