The existing D&D spells from the D&D Cyclopedia cover most magical effects already. New spells are often just minor variations of old ones. Bardolph’s electromagnetic barrier sounds novel, but if it measures 20' x 60', prevents the passage of creatures with fewer than four hit dice, and does 1-6 points of damage to all others, then it's not very different from a wall of fire or wall of ice. At least, it's not very different in terms of game mechanics. In terms of game atmosphere (how the players perceive it), it could be very different indeed!
This is the key to creating hundreds of new spells to suit any kind of spell-caster: make cosmetic changes to existing spells. Describe spells differently. Magic missile need not be a shimmering arrow. It could be a telekinetic fist, a jet of flame, or a steel pin stuck into a voodoo doll. The game mechanics remain the same. All that changes is how these effects are brought about. Hence, a magic missile variant will still do 2-7 points of damage, with a rangeof 150' and a duration of one round. A shield spell still grants a saving throw. As for the rest, use your imagination. Maybe Maximus the Black casts magic missile by momentarily enchanting his dagger, then making a pass at a distant enemy with it. A cut, doing 2-7 points of damage, opens up on Maximus' enemy, mirroring the swipe Maximus made with his dagger.
When you redefine how spells work, you may need to make some additional, minor changes for the sake of consistency. Maximus the Black, for instance, will always need a dagger or some other sharp implement with which to cast his version of magic missile. Such changes require careful thought from the DM and ought not to affect the overall power of the spell too greatly.
The benefit of this method is that there is no danger of upsetting the game balance. All the spell effects have been extensively playtested already. Redefining the causes just adds color, individuality, and panache.
Spells can also be styled so that they are in keeping with the overall conception of the character. As an example, take Illfrith the Ice Queen, a 5th-level magic-user NPC who lives in the DM's Northern Wastes campaign. Ordinarily, she would not be able to use any ice magic until she reached 7th level (wall of ice). Yet she can cast fireball at 5th level. By describing her spells differently, however, she becomes a real Mistress of Ice Magic.
Here are Illfrith's spells, with descriptive notes. Unless stated otherwise, all the effects remain the same as the original spell (damage, range, duration, saving throws, etc.).
First level
Magic missile. Illfrith conjures an icicle out of thin air, then hurls it.
Shield. Her skin becomes the bluish-white color of a glacier. Intense heat, as from a fire-based spell or large, open bonfire or furnace within 10 negates this spell.
Second level
Knock. Illfrith freezes any lock or bar on the affected portal, causing it to become brittle and shatter with the first use of force.
Web. Instead of sticky strands, a layer of ice forms over the area affected, immobilizing all within. The ice can be physically broken or melted with fire (standard 1-6 points of damage in the latter case to any characters touched by the flames).
Third level
Fireball. Illfrith creates a zone of intense cold (Fimbul-winter) in an area corresponding to a fireball’s standard area of effect. The duration is one round.
If you work backward from the effects to the cause, you will find that standard D&D spells can be transformed almost infinitely. So long as the power of a spell is not increased, anything goes. You can even change the name if it suits you. The D&D game is about imagination. Use it, and bring back mystical magic.
