- Level 1: mind, senses, obstacles
- Level 2: movement
- Level 3: cause damage
- Level 4: physical transformation, creation
- Level 5: conjuration/summoning, souls
- Level 6: large-scale physical changes, death
Most spells have "static effects" (duration, area of effect, damage, quantity, hit dice affected, movement rate, mass, or range) that do not change with the caster's level, but is always a fixed number or range of numbers. In some cases, the measurement was actually related to the spell level (6th level area spell that affects a 6" x 6" area, 4th level spells that blocks creatures of 4 HD or less.) In contrast, variable effects vary with the caster's level. In some cases, variable effects like damage seem to add to base spell level, but in other cases, I changed a static effect to a variable effect and counted that as a +1 level offset to a base spell.
For either static or variable effects, the units of measure (rounds, turns, hours, days for time, feet, tens of feet, miles for length/distance) is set by the type of spell, although units can be scaled up if a restriction is added (Hallucinatory Terrain covers a wider area than Phantasmal Forces, but can only create illusory terrain.)
The lowest level spells tended to be based on a natural ability that the caster could perform without the aid of magic, but with one restriction removed or altered in a magical way. For example, befriending a person without having to say something persuasive (Charm Person.) These tend to last longer or otherwise be better than spells that are unnatural versions of natural abilities, like Read Languages or Detect Magic. In the terminology I was using in the analysis posts, the latter spells have a "unnatural" Feature, while the former had either one Variable effect or a static effect with the units of measure upgraded as a Feature.
The Features I wound up using frequently were:
- removing or altering one additional restriction;
- expanding scope (allowing larger than normal targets + removing size limits altogether counts as two features;)
- adding or improving combat abilities;
- adding or improving control (including adding limited autonomy to otherwise mindless objects/entities;)
- counteracting one thing (each spell level counts as one thing;)
- narrowing a broad vulnerability (including replacing susceptibility to Dispel Magic with a specific counter-spell.)
- duration features: terminating condition is based on type of spell (sensory spells terminate when a sensory condition changes, etc.)
- length features: tied to spell level
- area features: tied to spell level
Re-thinking existing spells also led to some interesting new ideas for handling spells. For example, making Sleep accelerate the natural effects of fatigue in order to make it "fit the system" has the side effect of leaving victims tired even if they wake up quickly. Similarly, having Continual Light require a roll to maintain any time the surrounding lighting changes, and having Plant Growth require a reroll when the seasons change.
And sometimes just looking at the original wording suggests an entirely different way of handling the spell, as in the case of Clairvoyance and Clairaudience. On the whole, there's a lot of room to create a far more interesting spell system.