MOJam hatchet bow was a "one tool" contest, not even a pencil allowed. Rules were; hatchet, B-50 and beeswax. You were allowed to sharpen the hatchet as needed.
I was thinking of something like; most artistic or most bizarre or most snaky or most whatever but still able to shoot a 10 grn / # arrow 150 fps minimum. Or maybe bow made in one day or one hour. Or bow made from wood found within 100 feet of your house, or bow made from the weirdest found object or material.
None of these is quite what I'm looking for, but if we cast around some ideas, the good ones will float to the top.
Got nothing against the ambush bow challenge except that its been done and several of us did it back then.