Let me sketch out a world's magic system.
Rule of Four
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There are four schools of magic which compete with each other (and a banned fifth house which is underground). There is magic based on the four elements. There are four types of magic (Animal form, Geometry form, Emotion form, Primal form).
Magic is cast by speaking softly the name of the spell. The spell is then made manifest, and then the spell acts on the next action turn as a semi-independent Form.
Certain forms can decisively beat other forms. Certain forms can weakly beat other forms. This is known to everyone who is a magician. The typical magician who is not in a protected school is a professional.
Magicians duel for the honor of their schools (similar to old Kung Fu movies), and the honor of their particular teacher. In preparation for a duel, they stand fifty feet from each other, and use the spell Auralink.
This links their powers to create a battle circle which is a zone that prevents their magic from getting out of hand. It also has the effect at the end of a duel of enabling the winner to much more easily use the spell...Aura steal on the loser. Use of Aura Steal empowers the winner with extra strength and energy both physical and magical for several weeks. It imposes this cost on the loser.
It is possible to refuse a duel, and run away. The attacker may then legally try to aura steal, but its more difficult. Such flight gets one a bad rep too as a coward which is important in this culture.
It is possible to steal aura from non-magicians. They have little defense or understanding of magic (although most realize it exists, few have the talent and the willingness to become a magi). It offers less advantage than stealing from a magi, and the loser is often sunk in unexplainable gloom for several weeks. This is considered very bad among the four elemental Paths or Schools. Some schools sanction it in emergencies, and others not at all. However, the banned fifth school revels in it. The response of the four schools is to hunt the Five Magi down, and kill them (most normal mage duels do not end with death although that is a possibility).
The Sixteen Spells:
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Animal Form:
1. Water Horse
2. Fire Eagle
3. Earth Rhino
4. Air Cheetah
Geometry Form
1. Ball of Fire
2. Arrow of Air (Triangle)
3. Square of Earth (a fortress)
4. Line of Water
Emotion Form----actually I'd like a different type than this.
As an example Mage A is desperate, he's been forced back and back. His enemy is faster than he is, so his enemy has gotten in four spells to his three...and he's almost beaten so he does what most beginner mages do in dire straits...
Square of Earth he sings out quietly. Ten foot high, one foot thick walls of solid clay materialize out of the Nevernever around him. He feels safe.
Meanwhile his opponent guessing what he would do says Arrow of Air. And the Arrow of Air is a very weak attack spell, but unless stopped, it will follow you anywhere. And the Square of Earth has an open top.
The Arrow arcs over the fortress wall and slams into Mage A. He is rattled, and stunned, and loses his concentration and his Square dissappears.
Mage B attacks with Aura Steal as Mage A tries to focus after getting his bell rung. Its too late. The steal takes effect and A's energy and willpower flows out of him to strengthen the already stronger Mage B.
Now if B had guessed another spell, and attacked with Line of Water, a blasting roar of water like a fire hose would have appeared in front of him, and seconds later went off in a straight line at Mage A. And the Fortress would have utterly blocked it, and been undamaged.
As a verser side note: The verser would have great advantages with his own magic which did not follow the rules. Also, he would attract a lot of attention because magi would think he had discovered one of the fabled Lost Spells. On the bad side, most every mage he met would be a professional who was trained in quick casting.
And yes, I know thats pretty sketchy. Feel free to add more or modify...