This magic system would be a great way to encourage players to use different fighting styles.

Instead of removing magic you could change the way it works. A fire spell would be a fire ball during one moon and a fire stream the next moon. Very powerful magic items could act like moons, to allow players to keep using a type of spell.

The player can also be limited to how much powerful items they can wield, allowing them to keep only one or two spells the same.

Oh, gods damn it now I have the music from Ultima III running through my head.

Too many hours were spent idly waiting for the moons to align properly to open those magic gates.....

One, let me say this is a very cool idea.

WIth that said,

One someone could even have moons govern certain elements of magic. If the fire moon and a wind moon were out that night, only those types of spells could be cast.

In a game like this, would the following be applicable?

• If magic is governed by different moons, then I would assume that all the moons have the following: a heal spell, an attack spell, a defense spell, and a buff spell.
• All the moons have spells that are unique to that moon.
• if the player has a moon alignment, then if the aligned moon is out gives them a bonus powerup (to stats and magic) as well.
• If moon alignments have opposites, then a penalty 'powerdown' to opposing alignment (to stats and magic) is applied as well.
• There's a limit to how many alignments a person can have. Or is there?
• Fights during daytime are different than fights during nighttime.
• Is EXP used to level up stats, magic, or both?

If magic is governed by different moons, then I would assume that all the moons have the following: a heal spell, an attack spell, a defense spell, and a buff spell.

That COULD work, but core to the design is that the moons are different.

if the player has a moon alignment, then if the aligned moon is out gives them a bonus powerup (to stats and magic) as well.
If moon alignments have opposites, then a penalty 'powerdown' to opposing alignment (to stats and magic) is applied as well.

Why penalize a player who already lost access to some of his spells further ?

I would align characters (instead of players) to moons, and if their moon is down, maybe give them a buff to regeneration/defense to keep them semi-usefull.