More spell analysis, as I work out the bugs in the build-a-spell system. Notably, 3rd level is the first time in the LBB that we see damage spells.
Fly is Levitate (the unused "travel" version mentioned previously) plus the ability to steer. 2 Features + 1 Variable = 3rd level spell.
Hold Person is supposed to be "similar to a Charm Person" but it's easier to build it off Hold Portal, but for people instead of doors. Assume it's like physically restraining a person, but without touching them (cantrip-level effect) and a feature "magical binding can't be broken physically." That would be a 1st level spell; add variable duration and quantity (number affected.) This does make it shorter range, but potentially boosts number of affected targets if they are in a small area. 1 Feature + 2 Variables = 3rd level spell.
Dispel Magic is two features ("counteract magic" and "any spell",) but by the book doesn't contain any variables. Let's add variable area. 2 Features + 1 Variable = 3rd level spell.
Clairvoyance poses another kind of problem: do we go with the later interpretation of the spell, or what's suggested in the original wording? According to Men & Magic, this spell is the same as "[the] ESP spell except the spell user can visualize rather than merely pick up thoughts." So, it's not really the ability to see through walls, but to see what a creature on the other side of a wall can see. If it's unconscious or hallucinating, presumably you will see its dreams or visions instead. I like this, plus it's easy to implement (ESP + 1 Feature.) The same goes for Clairaudience.
Fire Ball I've mentioned before, but I've had some second thoughts. The underlying spell shouldn't be the cantrip level "start a fire without matches", but a 1st level effect "create an explosion of fire out of nothing." Since we have a damage variable, that leaves one other variable available, if we want to keep this 3rd level. Let's go with variable range, making the area fixed. Actually, we can turn a Fire cantrip into a fiery explosion with an area feature, similar to the duration features discussed last post. Make the area of an explosion fixed, but tied to damage, reducing it by 1 die per yard of distance from the target. That makes this Fire Ball version weaker than the D&D version, but still usable -- and not as dangerous in tight spaces.
Lightning Bolt has no explosion effect, but it has a fixed length and "bounces" if it can't extend its full length. We could consider that a "length feature", tied to damage dice, like a Fire Ball explosion.
Protection from Evil, 10' Radius is like the 1st level spell, but adds "area effect" (Feature.) But why is it 3rd level, instead of 2nd? Let's add variable duration to make it fit the pattern. Invisibility, 10" Radius adds just the area effect feature.
Infravision can be built from "unnatural sense" (Feature,) variable duration, and longer time unit for duration; we could do the same with Water Breathing, but with "unnatural ability" instead of "sense". Each is 2 Features + 1 Variable = 3rd level spell.
Slow and Haste both alter the time needed for all actions (Feature,) plus have variable duration and area. Each is 1 Feature + 2 Variables = 3rd level spell.
Protection from Normal Missiles might be underpowered, but let's try conceiving it as "provide a barrier against 1 missile" (cantrip-level) + "affects all missiles for duration" (Feature) + "impenetrable except by magic" (Feature) + variable duration. 2 Features + 1 Variable = 3rd level spell.