Heck, how about a 'smiley face' balloon challenge? Seeing smiling faces inflated to different sizes and the shooter(s) (and spectators) can eat fruit or something between shots to maintain their 'Zen'.
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This would actually be a fun but tough challenge. I was thinking about it last night. Those balloons will be dancing all over the place with the slightest of a breeze. You could put them on a stick versus a string to mitigate the majority of that, but it will still have quite a bit of movement. You could vary the size and height. Also, using a FFP won't allow you to range the by bracketing them because of the unknown sizes.
On a smaller scale, say 60 - 300yds, I also think this would be a great way to get kids involved, giving them basic fundamentals of trigger discipline, electronic ranging, getting their dope correct, wind reading skills and at the same time you're helping them extend their effective range. You could add colored chalk dust to the balloon prior to blowing them up for a no questions asked hit marker.
Plus, turn them upside down and they have a mini manbun for all the Creedmoor haters