Rift Keeper (EP)

They look a bit like bats, but are acutally flying books and are not really collectibles in a classis sense, because there are inifinity of them and there are not well hidden. You can found a couple of them each stage and you don't need 100 in your inventory, because it also count's if you use them for random items. I suggest to keep all of them to use a save trick for the legendary items later.