After blowing up Belial at the end of chapter 7, you have to escape the weirdo cloud place while being assaulted by triggered Belial spawns and gargoyles. New baddies appear in the mansion. The last time you see Belial during the intro sequence, he blows up and releases a pesky seal that's been on a door since the beginning of the game.
There's a room where you summon a goofy thing by lighting 5 candles.