While luring Stay Puft around times square you will enter a building. As you make your way to the top you have to go through a large room where you will need to fight a small horde of marshmallow minions.
Kill all the creatures and then carry on trashing the whole office, smash anything and everything in sight that will break, this includes windows, pillars, desks etc. If you see the damage counter keep going until it stops counting. Open the door to carry on, you will have to fight more minions, use Boston Darts and trash whatever is in the doorway.