There is one of 20 voodoo dolls in each level. From the main menu, you can go to Help & Options, then View Collections to see which levels you have either the tarot card or voodoo doll in, and which levels you still need them. Dolls can appear hidden in bins or other punchable items, so make sure you look everywhere. For the item collected to count, you must finish the level, but one thing I always found handy is that you can finish the level, then just search around after your done, so no zombies attack you.