Now, I don't have any code down in the game yet, but it is all written down on paper.
Here's the basis of my Crystal System for my Final Fantasy fan game:
After a certain point in the game, your character can equip one crystal at a time. The crystal will add abilities,stats,etc. to the character it is equipped on. There are several different types of crystals:
~Ability/Skill
These add an ability for the character to use. Such as a Black Magic Level 1 crystal would add the ability for that character to use level 1 Black Magic.
~Add Effect
These add effects to the Attack command. Such as Mug would have your character(Zidane) steal when he attacks. Double Slash would have your character attack twice.
~Level Ups
These add a permanent stat increase per character level up if that crystal is equipped during level up. Such as, Strength +1 would permanently add 1 strength to the character if the crystal is equipped when the character gains a new level.
~Passive Increases
These add a percentage increase on stats overall. Such as, HP+ 10% would add an overall 10% increase to max base HP.
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After each battle, crystal points are earned. These automatically go to the crystal that is equipped on each character. Virtually, every crystal can gain a new level once it's crystal points have been maxed for it's current level. Such as a Vitality +1 crystal levels up so then it becomes Vitality +2 and the crystal points reset to let that crystal gain an entirely new level.
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Each character will have ability points each to his level.
Every time a crystal levels up on a character, that character permanently knows the previous ability of the crystal. Such as HP+ 10% gains a new level, the character will permanently know HP+ 10%. The player will then use the available ability points to equip that ability to himself. Different kinds of abilities will require different amounts of AP.
This would allow characters with a Strength+ 2, HP+ 30%, and Vitality+ 1 abilities equipped while he has a White Magic Level 5 crystal equipped in his crystal slot.
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When a crystal levels up, it only levels up for the person it is equipped on. So, say you have HP+ 10% on Tidus, and it levels up. Only Tidus will gain the new +20% from the crystal. If you move it to another character, it goes back to 10% unless they have already learned +10%.
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tl;dr
Think FF6 Esper System + FF7 Materia + FF9 Ability System
I think if I can do it properly, it would allow for some pretty in-depth character development with attributes.
What do you guys think?