A possible situational addition for the moon phases could include something like the following:
Nercuros is very large in the sky and always full, lending to the idea that it has the strongest impact on gravity. Under this moon:
- Plumbum Manus gains increased effectiveness in combat
- Localize weapon and disarm gain increased effectiveness, perhaps even with a chance of overcoming noremove (though that may be too strong)
- Meteor Swarm cause bonus damage due to the heavier impact of the meteors
Dyphrities is small and dark, and very difficult to see by. Presumably the gravitational pull of the moons in orbit is weakest when Dyphrities is high, so:
- Path of deceit and chorus of anguish are stronger when Dyphrities is in phase.
- Blanket of Darkness (shaman spell) covers the current room and any adjacent rooms when used
- Phantom grasp and ghoul touch have an increased chance to land
Lysenties is extremely bright compared to the other two moons.
- Sear can be used effectively at nighttime under the light of the moon
- Colour spray, ray of truth, and flashfire gain a heightened chance to blind due to the increased lunar light
You could then increase these bonuses 50-100% for Lunareth due to their attunement to the moons.
And of course you could contend that the opposite effects (i.e. disadvantages) occur under the presiding moon's counterpart. However, I think most importantly this represents the opportunity to create situational boons for lesser used classes and race/class combinations without drastically altering the class as a whole (e.g. battlemage and both clerics).