I've actually been thinking of making a magic mod for DF, so perhaps we can use some of the ideas I came up with.
First of all, the main ingredient in all spells, magical tools, and alchemical constructs is mana, which can be stored in solid form as "mana crystals." There are various kinds of mana, fire, water, earth, lightning, etc. Mana can be obtained in several ways:
- Killing and harvesting the corpses of mana elementals. (Mana elementals will also have different types corresponding to the mana they produce.)
- Finding it in loot chests (Ranger's Guild gets to place these.)
- Extracting it out of the environment (atmosphere, ground, water pools, volcanoes, etc.) using certain tools in magical biomes. (Ranger's Guild also has authority over the placement of these.)
There are also various other ingredients -- "astral dust" can be made from grinding gems, or is found in bags as loot. Spells are actual physical objects, which can be crafted, and have to be stored in crystal orbs to not vaporize instantly. Certain spells require ingredients which can only be harvested from special creatures -- shield spells could need the shells of "perhons," creatures which are nearly impervious to most kinds of magic. Spells have different tiers depending on how powerful their effects are. Spells are fired by wands -- essentially twigs with runes carved on them and plastered with astral dust. Wands also have different tiers -- the higher tiers have higher ranges, higher firing speed, and are able to fire more kinds of spells (wands can only fire spells whose tier is less than or equal to their own.) There could also be specialized wands, wands which can only fire one type of spell (only shield spells, or only fire spells) in exchange for higher wand quality and easier crafting requirements.
Another idea I had is that by combining "elemental shells" (have a small chance of being obtained from the corpses of mana elementals, and can also be crafted) with mana and various other ingredients, you could be able to summon your own mana elementals which can fight for you.
There would also be several alchemical contraptions, for extracting mana from the environment, purifying materials, etc.
If we go with this system, we probably need to compile a list of mana types, as well as a list of basic ingredients and how they can be obtained. Then we need to write out a list of spells, and design the wands. (We could also perhaps design some magical melee weapons; I didn't think of any because those aren't really possible as a DF mod.) Then we can go on to the more complicated things, like summoning mana elementals and doing alchemy.