Complex sentence: Changelings are often described in Western European folklore as a type of legendary creature, left in place of a human infant, for a variety of reasons, usually not able to mimic the human perfectly, there various ways to reveal them.
Split into simpler sentences: Changelings are often described in Western European folklore as a type of legendary creature, left in place of a human infant, for a variety of reasons. They are usually not able to mimic the human perfectly, thus there are various ways to reveal them.