Granfalloon

This dude is nothing but a huge mass of bodies around a core that throws off lightning. Destroy that core by exposing its belly. Soul Steal will really help if you have HP problems in this fight. As for sub-weapons, go for the Axe or the Cross. When you hit him, corpses will fall down from the gigantic ball. They're not a problem though, other than their sheer numbers. Focuse on creating a hole to the core and striking it. He's in the Catacombs.