And/or that one Lore Charm.
That strikes me as
exactly what God-Kings Shrike is for, or should be used for at least. It's perfectly suited to playing a prophet who threatens a ruler that great doom will befall his nation unless the ruler recants his decadent ways (or somesuch), and it allows you to do that, including taking back the prophecy before the catastrophy happens.
Granted, it only works once per year (or season if you spend a ton of XP), but that just means you have to rely on other options.
- Turning a river to blood: done via Eclipse-keyword spirit charm
- Frog-swarms: would be a fitting Celestial-Circle spell if it's widespread. Maybe Terrestrial if it's a widespread but only annoying effect, and reasonably short-lived.
- Flea-swarms: again, a spell would work well.
- Swarms of flies: yeah, same again basically.
- Plague that affects all lifestock: well, an effect that releases a plague might be a high-end medicine charm. Or again a spell. Or a Soulsteel-artifact maybe. Or negotiating with/coercing a disease-spirit would work too obviously.
- Plague of Boils: again, something that releases a plague.
- Large thunderstorm: Weather-control magic is a thing in Exalted. Spirit charm or Sorcery work well, but it could also be an artifact or a charm (though I don't see it as in-theme for Solars). My favorite to get a "thunderstorm of hail and fire": summoning some elementals!
- Swarms of Locusts: gee, another bunch of small animals. Though this one is more destructive
- Unnatural Darkness: Impenetrable Veil of Night is a Celestial-Circle spell, though it only has a one-mile radius.
- Death of Firstborn: This can be accomplished by a lot of means. But it does fit well with the large-scale prophecied catastrophy, except that it is maybe too discriminating.
Of course, what the Plagues of Egypt would be is a priest who is very close to a high-ranking god. The priest makes some prayers, the god provides the effects via his own charms, or by getting local gods to do it for him.
Sorcerous Workings do not fit well since those take a long time to accomplish AND have long-lasting effects, while all of those were temporary.