If it's just for a weekend, you could get crazy. Like...

Curse of Moo-re Cow
It's just the right moon, or perhaps the weather! Maronessa's curse went contagious, infecting humanoids. You have to find the right elements to help keep the contagion under control. (Excuse to meet weather-witch characters, each level group could need a different cure, meaning a different creature or zone to seek out the cure in. And of course, lots of whining from the elves in Serbule!)

Yeah, it's like the bat curse, but if it's just for a weekend, well... If the mechanics are set up, this could be a re-occuring thing in different flavors (deer, pig, spider, etc) and solutions (Fae, alchemy, crystal augury, etc)