I also read stories like that as a child. I saw several videos about them on youtube that used to say that they are supposed to be a spirit, like a "son", that they do good and bad mischief, but that they never hurt the owner, something like that.

Thank you to everyone who responded. I asked this because there was no topic that answered that question completely. Lately youtube recommended me a video about it which left me with a certain doubt.

Lately, I've been thinking about this issue. I know that many people have a leprechaun that lives in a bottle (to get images just search “GARRADUENDE”), basically they say they are spirits that play with you, do you good and are your friends. The question is, what exactly are they? The...