How rare is a full moon in blox fruits?

Could you elaborate on the rarity of a full moon in blox fruits? I'm curious to know if this phenomenon occurs frequently or if it's a rare occurrence that players should be on the lookout for. Additionally, what significance, if any, does a full moon in blox fruits hold for gamers and the in-game environment? Lastly, are there any specific events or activities that are tied to a full moon in blox fruits?