Submission: Magic mechanics in the world of Change, my WIP tabletop RPG.
In my setting, Change, magic's purest form is called "vitae", an energy originally believed to be a kind of life force. It's produced my most living things, and it can be used to shape and transform other energies. Most living things cannot create vitae, this is a role normally reserved for plants, but vitae can be gathered from other living things, transferring from one living thing to another through the food chain. Vitae gives an innate advantage to life, because as it radiates out, it richens the world around them. By default, it just promotes the growth of vitae-using plants, and is responsible for the mega flora of most settings, but many planets have formed avatars with their surplus vitae to oversee and guide the world, and protect it from threats. These avatars are gods, and they are a force of nature given form and thought.
Normally, living things have no control over their vitae and cannot use it, and simply radiate it out should they have more than they need. It can only help them by helping the ecosystem. Sapient beings are different. They don't radiate out vitae, they hold onto it, and they can use it. Vitae can strengthen the user, change their physiology or grant abilities, and can also be given to others. (In game, that means it can boost your attributes, grant perks or teach you spells, and can be used as a currency.) The abilities granted are spells, and spells comes in four categories, each distinct from the others in philosophy, method and application.
Nature magic uses vitae to control nature, granting the ability to heal living things, shield the user from harm, project chemicals and control animals. Arcane magic uses vitae to control energy, attacking with the elements, moving objects and creating elementals. Divine magic uses vitae to manipulate the mind, mostly controlling emotions, but also altering memories and even pressuring others into actions, as long as they're unaware of it. Occult magic is the collective term for magics outside the others or mixing them, being able to alter matter, manipulate time and space, raise the dead, summon beings, drain vitae and dispell other magics.
In order to use a spell, first you have to learn how it works. Then you have to tribute vitae to form the basis of the spell for later use. This takes the least vitae for nature magic, the most for occult, with it taking the same amount for arcane and divine. Then you can use it, but the template has a limited number of uses that replenish each day, with more powerful spells being usable a smaller number of times. You'd also be well served to know what part of the mind will enhance its effects. Nature magic takes resolve, arcane magic takes perception, divine magic takes charisma and occult magic takes all three. Magic also has a cost per usage, as well. Nature uses just vitae, arcane uses vitae and tires the user, divine uses vitae and injures the user's mind through the backlash, and occult magic uses vitae and causes the user injury by combusting their blood.
Due to the limits of magic in this setting, and the other possible uses of vitae, spellcasters aren't innately more powerful than non-spellcasters and have to think and plan how to make the most of their magic to make it as effective as it can be. It's useful, but it's not game-breaking. This is further reinforced by the fact that anybody can learn magic and most people do, but they still make sure to learn other skills. I prefer this, because this setting is the setting of an RPG, and it does wonders for balance while still having a believable world and no gameplay/story segregation.
