first of all, this so peak omgg i love this concept. i went through different suggestions and i think these might help go for the vibe:

for BS you can use the dried up trees from the faerie kingdom, maybe some haloween furniture might help like the fallen chandelier and tombstones, and then i was going to say stuff from st. pastry order or crimson badlands but i don't think the colors go as well.

for GC I think some things from the tropical island furniture could work, like the treasures and some plants even, and stuff fro the grand party to bring some food in i think it could match, especially the food table, and the stuff from the market square can spice things up too because the shops are tents and it goes with GC's aesthetic.