The string that grants 3 wishes once it falls off is actually based on a real Brazilian tradition, just not as creepy. There's a popular church in Salvador, Bahia that people visit from all over and they sell colorful ribbons that say "Lembrança do Senhor do Bonfim da Bahia" (Remembrance of the Lord of Bonfim of Bahia). The tradition is to have someone tie the ribbon around your wrist, making three knots and with each knot you make a wish. People will wear it until it gets really old and falls off by itself, which is how your wish comes true! You're not supposed to cut it off either, like the trailer describes.
No character appears in every episode.