Blood Moon
With the new targon lore, we are presented with celestial aspects: War, Sun, and Moon, silver moon to be more precise
A blood moon is a moon eclipse that causes the moon to become red because of the shadow of the earth projected on it.
Looking at Udyr's lore, the blood moon seems to be a time where the spirits realm and Valoran are closer, that's why Udyr, having been born under it, became a "Spirit Walker", but there is something more about the blood moon, all the skins related to it.
At first it would seem that they are champions posessed by spirits that come from the blood moon, until you see Thresh and Kalista, that are ghost...posessed by spirits? It doesn't seem possible
With Diana's new lore, we get to know that every aspect can grant powers to some chosen champion, and modify its look to some extent. the only one that wasn't specifically seen was the Moon aspect, only a old women that disappeared as soon a Diana reached the top, while Pantheon and the golden boy guided their champions to the city.
Could it be that the Blood Moon skins are all champions posessed by the aspect of the Blood Moon? while Diana got the one of the Silver Moon, the purest.
This would make the Moon aspect one with more than one personality, a silver, pure one, and a blood, corrupt one, maybe by the efect of another dimension or The Void itself
I know that skins are usually not lore related, but it seemed too interesting to let it pass by, as this could mean that while Valoran is fighting against The Void, (or whatever that great danger might be) many champions could turn on everyone and make the situation grow really dire (With Diana as the most powerful, as she had been blessed with both the silver and blood Moon aspects)