Faeries are pranking mortals, so I need to align types of pranks with the 4 elements/humours/temperaments. My idea is that certain sorts of pranks will more align with certain elements, and therefore be opposed by the opposite. So, frex, making someone angry aligns with Fire, therefore the  difficulty for the roll would be determined by Water score. That's the basic idea. But since it's Titania and Oberon that the faeries are trying to impress, rather than the targets of the pranks, it's more about how the pranks are seen by an outsider, rather than the impact they have on the target.

Coming up with a complete theory of [faerie] comedy turns out to be difficult. ;-)  Here's my preliminary work:

Sorts of pranks:
Slapstick: resisted by melancholic
Cleverness (wordplay, witticisms, etc.): resisted by ??
embarrassment: resisted by phlegmatic
satire/mockery: resisted by sanguine
cruelty: resisted by sanguine
misleading/entrapment: resisted by choleric

For these purposes, I was using Wikipedia's definitions of the four humours:
Fire (choleric): angry, bad-tempered
Water (phlegmatic): calm, unemotional
Air (sanguine): courageous, hopeful, amorous
Earth (melancholic): despondent, sleepless, irritable

Biggest problem is that, right now, I think I have a muddle of techniques and affects. Though maybe that's ok, so long as the players can clearly categorize a given prank. Any suggestions on categories of pranks?

And maybe I'm trying too hard on using the humours/elements for this, and should just give the sovereigns scores like "empathy" (used to resist being impressed by a prank that hurts or embarrasses a mortal) and "dullness" (used to resist witticisms)?