What about solar eclipses? They would happen 1 day every 100 days, and during them the environment would be dark, as it was night. As a result, monsters would spawn :Spider:.
On the other side, lunar eclipses would cause massive floods (the water level rises up to 10 blocks) and spawn werewolves (wolves that become automatically hostile when they see you) or red creepers , that put casually on fire some blocks around while exploding.
On the other side, lunar eclipses would cause massive floods (the water level rises up to 10 blocks)
This has been suggested, but as a red moon. I like these sorts of ideas though.
Now, if you'll excuse me, I'm going to walk away before muncher gets here.