Has anyone played around with Spell Thematics at all? It's an interesting feat that actually looks like straight up garbage until one futzes around a bit.
It gives +5 to DCs for spellcraft checks to identify your spells, and lets you pick a theme. All your spells display that theme, with the examples given as 'fire, ice, screaming skulls', and some actual language detailing that.
The first example is a 'fire' themed mage casting Magic Missile. The missiles look like bolts of fire.
The second example is a 'screaming skulls' themed mage casting Fireball. The fireball looks like a skull. It screams (producing actual sound, but the sound doesn't add the sonic descriptor or anything), and when it detonates, the smoke cloud takes the shape of a giant screaming skull.
From these examples, we can discern two things.
1. This feat adds visual manifestations to spells. Corollary: This feat adds visual manifestations to spells that don't have visual components.
2. This feat can add sound-based manifestations to spells. Corollary: This feat can add sound-based manifestations to spells which don't have sound-based components.
The theme you pick is fixed, but you can be pretty creative with it, based on the listed examples. The reason this is interesting is because this feat can do things like add sound to a Silent Image, or a visual effect to a spell which normally lacks it.
Like, oh, I don't know, Locate City?
Why is this important? Because if you're a Dread Witch, you have this lovely feature:
Fearful Empowerment (Su): Starting at 3rd level, once per day you can add the fear descriptor to any spell you cast that has some sort of visual manifestation. For example, you could apply it to a fireball, to a summon monster spell, or to any visual illusion, but not to charm person, since that spell does not directly create any visual effect. Creatures targeted by a spell modified by fearful empowerment must make a Will save (DC equal to 10 + your class level + your Cha modifier) or become shaken for 1d4 rounds; this is in addition to any other effects the spell might
Using this allows you to basically make EVERYONE shaken, and if you're also a third level Nightmare Spinner, inflict 1d6 points of nonlethal damage on them. Which for say, commoners, basically lets you knock everyone in the area unconscious.
I'm not sure that this is super relevant to anything but a campaign's BBEG, but being able to knock an entire kingdom unconscious is nothing to sneeze at.
But wait, there's more! If we apply the metamagic feat "Fell Frighten" to Locate City, enemies that fail their will saves and take the 1d6 subdual damage are shaken again, escalating to Frightened, for one minute. They attempt to escape the spell radius by any means possible, including magic. This becomes a fantastic way to get rid of casters, since they'll either teleport or plane-shift out of the affected area if they fail their save.
If we apply the metamagic feat "Fell Drain" to Locate City, all creatures that fail their save gain a negative level. Any creature with only one Hit Die immediately dies on the spot. So basically most small animals, and the entire commoner community of the area.
Remember how I said this would be useful for a BBEG? Here's why: If we apply the last of the fell metamagic feats, Fell Animate, to the spell, it takes up an 8th level slot, and any creature killed by the spell rises as a zombie at the start of your next turn. Of course you can't raise more undead than twice your caster level, but that's what ludicrous caster levels via Circle Magic are for.