Magic varies from story to story, but in most universes there's a price to pay for magic. The RPG system D&D sums it up three very ellegant categories:
- Vocal: some magic words, like Abracadabra;
- Somatic: some gestures, like those required in early Naruto jutsus;
- Material: some stuff, like bat wings, rat tails or fresh tears from a virgin.
I'm proposing the metaphysical component.
This type would be composed of things that can't really be touched or measured, like emotions, thoughts or even memories. Some good examples are:
- A traumatic memory;
- A fresh idea...
The rules for you to propose a component are simple:
- State the spell you want to cast, like Expecto Patronum;
- State the component this spell will need, like a happy thought;
- State why is it needed. Our example works because dementors feed on happiness;
- State the effect the spell has on the caster. If happinness is consumed, is the caster suddenly sad? Tired? Unable to laugh for x hours/days?
- State a side-effect in case the spell backfires. Ideally, this should be a much worse cost than what you stated in item 4 (the caster gets heavily depressed. Suicidal even!) in order to keep things coherent, but feel free to make any kind of side-effect, as long as it's very bad.
You can choose any spell you can think of but if it's not a generally known spell (like casting a fireball) you have to explain how it works.
You can use as many components as you deem fit (even non-metaphysical ones), as long as you give a good explanation for them to be required by the spell.
It is not required that the component comes from the caster himself. So if you propose something like true love, the caster can use a young couple as his components. If you choose to do so, remember items 4 and 5. They apply to everyone involved in the spell but you get to decide how harsh they are for both the mage and his components.