NEW MONSTER ALERT.
These are some Ethereal Beasts (the somewhat more malicious cousins of Fearsome Critters). Occasionally called "kelpies," these creatures spend their lives beguiling frustrated individuals (for some reason they are most attracted to angry young people) with their natural wit and charm, which they use to convince their prey to climb onto their back. As soon as any foolish person does this, the Kelpie proceeds to run off with them- racing faster than the wind- taking them to incredibly strange (often desolate) places (and sometimes new worlds entirely), where they abandon their prey to die miserable, lost and alone.
As a side note: There are two kinds because I wanted them to fit in with the rest of my ethereal mythical monster pairs (see: Manticores and Aaish'ya). However, they have no set sex or gender, so any appearance of dimorphism is a trick. NOW YOU KNOW.