Yes, somehow, given the choice of spending their next diplomatic assignment at either The Spider Swamp, Crater Town, or The Desert of Cosmic Horror, our envoys decided that cosmic horrors would probably be more amenable to diplomacy than spiders or alien puddings.
I suppose if you're going to be negotiating with the unknowable in any case, it is reasonable to go big or go home.
Upon entering the desert, we quickly converted to the characters to a loose version of Call of Cthulhu. At first, I wasn't sure it was working, but sure enough, as time in the desert wore on, even the simplest kinds of banal monstrosities D&D adventurers otherwise take for granted (corpses, bloody altars, strange runes) took on new meanings. And sanity scores slowly dwindled.
Only when the diplomats sailed into the underworld did their dependable D&D stats return. I don't think I've ever seen anyone so relieved to enter the kingdom of the dead.
In the end, the diplomats dealt with the usual mix of diplomatic challenges.
- strange stars above the desert, uncountable, unrecognizable, wrong
- silent jackals, always watching from the next dune
- an archaologist from another world, gone quite mad and making terrible sacrifices upon the altar hidden in his tent
- the archaeologist's shadowy double (demon? ghul? doppelganger?)
- runes of the crawling chaos, messenger of the outer gods
- a trap-filled pyramid, of course
- mummified guardians inviting the diplomats onto a funerary barge
- the black river to the underworld
- the shade of the great kingdom in the underworld, safe these long eons from the crawling chaos
- the boy king and god of the great kingdom, who was happy to negotiate, for all the good a dead king's alliance will do them in the face of cosmic horrors above
To their credit, the diplomats were also smart enough to politely refuse the pharoah's kind offer of a meal at his table.
Ah, the life of a diplomat!