Had another game (which turned into a 2-parter). Both this one and the last were technically only with my son, but he played my daughter's pixie while she was at Disneyland, and we hope she'll be rejoining us after she's back.
The archdruid sent them to investigate more disturbances in the northern forest, as rumors of strange creatures seemingly appearing from nowhere and rampaging across it are spreading. They fought a dozen blightborn (UE) grimlocks, and then faced off against a mysterious skeletal figure accompanied by a blightborn grey render. They lucked out and no one failed a fort save against the disease, and although they prevailed, the mysterious figure (who used mysterious powers... i.e. psionics) escaped in the end using teleportation magic. He was silent the entire time, and so they have no idea who he was or what he was doing there, but they suspect it was nefarious because he was obviously undead and his grey render companion was infected with the blight.
My son's comment was "You're going to make me fight an evil druid in the end, aren't you?" to which I of course replied "Maybe..."
I'm thinking about having undead psionicists be a "thing" that's associated with the blight: i.e. the "elite warriors" of the power behind it will all be undead psionics users of some kind. I was also inspired by the "quietness" of this one, and am thinking of having them all have their mouths stitched shut as part of the ritual to make it extra creepy (but worry this might be a bit too extra creepy for my kids...)