You have to defeat all enemies in all rooms first to avoid being attacked while collect all of one colour leech charms and make it easier for you. Do it with Billy, because he is stronger against attacks and can deal more damage with grenade launcher, shotgun, magnum and custom handgun. After all are defeated, you can search up all rooms with Rebecca and collect her green leech charms. If you have all 50 in her inventory, you can leave the mansion at the door in the main hall. Can be done on any difficulty as long as you don't collect one of the blue charms with Billy. Trophy pops at the screen after you have left the mansion.