>>314880810I have beaten him with three different characters. He's not very hard really. He's got ridiculous amounts of HP, but he's really bad at damaging you. The only thing to look out for is the big coins, which you have to destroy before you get swarmed. You have 5 (or is it 6) floors with devil deals to get a strong build, it's a pretty simple mode.
Look forward to trying the new boss after the heart which I have no idea how I triggered 
