A Dark Moon is when the moon is in lunar eclipse phase, it is mostly black & will shadow the sky of stars for hours. The spell of a dark moon is also black/dark magic that is deeply powerful & too dangerous for any wizard that is not within the Top 3 Best to grant as it would cut deep into the wizard's soul if not performed correctly & could execrate them. A god however, can summon a dark moon, Dark Moon's black magic can be blocked or countered by that of a burning sun & vice versa.
Legality by the League of MagicEdit
It is unknown when, but the summoning of dark moons was made illegal by the League of Magic as it was symbolizing dark wizards. Anyone who casted one were charged with committing dark larceny, or the crime of committing an act of evil or dark magic. Three known dark moon spells casted were by Michael Desjardins before his arrest, Grimlon after the duel at Flame Temple & Talroc during the beginning of the Battle of Mexico.