My personal thoughts on the magic system for everybody to judge.
1.0 Magic should be the manipulation of mana (or something) and spells could be player-made.
1.1 Spells could have a casting-time based on how much mana is being used and mana-cost based on the same thing and the steps included in the spell. For example if someone wanted to cast a fireball they might have to write
"gather X mana, give mana fire properties, push mana forward"
the main con with this way of doing it is that most spells would be too limited and the only pro being that one more piece of the game would be player-made.
1.2 If you do a certain step enough times you master it and it decreases the cost of that step.
2.0 Spells should be either discovered by the player through experimenting or taught through a mentor.
3.0 People who have magical abilities should constantly let out mana when they haven't used their powers in a while which would have effects on their surroundings and if left unchecked could even be seen as an aura.
3.1 There could be a ring or an amulet that would stop or at least slow the effects of the mana so magic users could hide more effectively.
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The main reason I'd like to see a player-made magic system is that it would be interesting to see how spells evolved as the game aged. Please feel free to tell me if/why any of my ideas are dumb and mention ideas you've had.