Stop reading right now if you don't want spoilers. In order to get the best ending, you need to consume 3 parts of the umbilical cords that you will find throughout your journey. Some will be given to you after boss fights and others you will have to find in Ioseftka's laboratory. Once you consume these three items, fight the final boss and after you defeat them, another boss called the Moon Presence will appear and once you defeat it, you will get the true ending and one of the weirdest sequences in gaming.