-The fight takes place in a cathedral, on the bottom floor first. On the left and right sides of the room are switches, one on each side. These switches activate bells that disrupt Marcus' concentration and leave him vulnerable for a short time. Hit one switch, then run to the other switch, hitting Marcus on the way. Continue this until his "puppets" disable the bells. Go up to the second floor. Marcus will just run around until you kill him. Use the jump ability to alternate between sides, hitting him on the way. Once he dies, you acquire the Charm ability.
-Simply hit the bell switches and hit him when he is stunned. When his puppets disable the bell, you can still ring it by jumping into it. He is easier to locate that way. Then, just run around killing enemies while hacking up Marcus, sometimes ringing the bell. You can avoid the puppets altogether, but you will want to build up your Lore bar as much as possible.
-To defeat Marcus follow the previous strategies until his "puppets" break the bells. After that, pursue Marcus until you run into his "puppets". Kill the puppets, increasing your Lore and Blood bar. He will be on the same floor as his "puppets" -- this will help you learn where his next minion is located. When you find him, use combos repeatedly until he loses.
-Chase him into the room that has two switches on each side, then run to a switch and use it to ring the church bells. This will temporarily paralyze Marcus. Attack him with combos and the Fury power. When he recovers, run to the switch on the other side and ring the bell again. Keep doing this until he summons the bishops. Run upstairs and attack the guard, gaining any lost blood and weapons. He will be invisible, but will occasionally reappear. When he does, chase him, then attack him. You can still hurt him while he is invisible. He will summon more guards, but will be defeated before long.