So I wanted to give the players a reason to eventually go to the moon. But this is a fantasy setting, so having the moon just be a big rock floating in space would just be so.... blasé. So I came up with a system where the moon is a giant battery storing up solar energy until it expends it on the night of the full moon to push back the forces of evil and keep them from entering our world for one more month. The moon's phases are pretty much a giant battery icon in the sky.
I've got a few plot points lined up where the bad guys do various things to mess with the cycle, culminating not just in visiting the moon to fix a leak, but going to the sun to... do something with sunspots that I haven't figured out yet. Whatever it is, the sunspots are a natural cycle that the bad guys have been preparing to exploit. The point is, everything lunar (and possibly solar as well) is a potential plot point.
Which brings me to the tides.
So far, what I've got is that there is a magical artifact (or possibly a pair of magical artifacts) under the sea that moves along a track to stay directly under the sun at day and the moon at night, alternately collecting and discharging energy to/from the sun/moon. While the artifact is under a region of the sea, the excess magical energy raises up that area of the sea, creating the tides. The first sign of something evil afoot is that there is a problem with the tides, probably that they are low or off-cycle, I haven't figure out what yet. And the way to fix it is to travel to the track under the sea and fix whatever is being done with the artifact.
The thing is, something feels off about this plan. Maybe it's the fact that I want the world to be a plane, I don't know. That seems to require a charge/discharge cycle instead of merely facilitating redirecting solar to the moon, which I would prefer because it would only require one artifact instead of a pair (though a pair might need repairs to be conducted at either high noon or midnight). Or maybe I feel like there's something better that I can't see right now. Whatever it is, I was wondering if anyone might have any ideas to help me polish this up a bit.