Leprechauns

Physical appearance
It's unknown what they truly look like, or if they have true forms at all, but they can take on human form.

Powers and abilities

 * Magic - Being a creature made out of magic, Leprechauns are "all about energy," and can sense if someone's soul is missing.
 * Super strength - Leprechauns are extremely strong, being able to overpower humans with extreme ease. One Leprechaun quite easily toyed around with soulless Sam, to the point where he gave up and as the only way at the time, spilt salt in front of the Leprechaun, giving soulless Sam time to recite the fairy banishing spell, sending him back to Avalon.
 * Teleportation - Leprechauns can teleport from one place to another in the blink of an eye.
 * Invisibility - All fairies are invisible and can only be seen if they want to or by those who have been to Avalon.

Weaknesses

 * Grained substances - If a grained substance is poured in front of them, they are forced to count each individual grain.
 * Iron - Iron is very harmful to fairies, therefore including Leprechauns.
 * Cream - Fairies love cream, and it can be a way to easily appease one.
 * Silver - Dark fairies can be burnt with silver, it's unknown if all Leprechauns are dark, but at least one of them was, who Sam was able to burn by cutting him with a silver knife.