I think it has something to do with getting all the purple meatballs to the characters arena, IE boxer in waterfront, ect. Since one meatball follows each character, try taking one meatball to each characters ritual area or to the cirlces we use to do the sword upgrade. Kill them there with an upgraded arnie (also purple)? I would try this but I recently moved to the middle of nowhere and have to use an LTE hotspot for internet, and it only gets one bar. No ISP's where I'm at :(. Multiplayer is NOT an option lol. I can do solo online, thats about it.