They may have some harvest festival or something. I don't know... the holidays would come pretty fast on our calendar as their years go very quickly.
Well, perhaps you could have larger holidays to represent real world holidays? I know some holidays are celebrated for weeks at a time(though they're hard to look up). Perhaps some sort of astrological phenomena could signal the holidays in Mythruna? There are rare phenoms that we celebrate like eclipses and meteor showers.
For easter, perhaps breeding season for some sort of animal; cicadas mate every 17 years, for instance. I keep thinking they'd have opaline bones that could be made into stuff. They could be some sort of subterranean beast, like the mole rat or something, to justify their randomly appearing... Perhaps a smaller planet comes near to the mythruna earth, that has some sort of influence on them...
Like, for halloween another planet may align with the mythruna 'earth' and cause an eclipse for all of halloween and people would celebrate something related to the eclipse(maybe celebrating a plant or plants that only bloom during the eclipse -- used to make sweets, perhaps?)
For thanksgiving there could be a second moon that appears -- or perhaps a solar flare hitting the planet causing a
geomagnetic storm. In other words, a gorgeous. warm aurora that also wreaks havok on electronics... But it's basically the sun shooting energy at the earth so having it be a REALLY big harvest festival or something may work...?
And lastly, for christmas, perhaps the planet drifts into a belt of crystal rich meteorites, and the sky glitters for a while. The npc wizards may cherish this day more than others. It certainly would be interesting if meteors hit too, but that may be a tad destructive... xD
Just some ideas. It would certainly motivate people to hop on on the holidays... and would be better than Minecraft's bs gift box chests on christmas. >.>
