My old hall in the '70s had these awful plastic bushes on either side of the stage. They were tall and there were so many of them that it looked like a jungle.
I took some Barbie dolls into the hall during cleaning night and posed them as if they were climbing up the trees in the jungle.
The next morning for the Sunday meeting I kept my mouth shut, but soon you could see kids whispering and pointing. But, they were camouflaged enough that the elders didn't notice them before the meeting.
Afterwards I managed to rescue them from their jungle expedition with the elders none the wiser, but the kids were laughing their asses off. It was th most fun they had at a meeting since....ever!