Do you just work it out with everyone at the table how stupendous a feat can be? My son is pretty young and imaginative, which is great, but he's also keen on wining... even if it means being stupendously ridiculous. Is the idea to just get away with as much as everyone else will let you get away with? Or do you guys really let anything go as long as they make the roll? There's no inherent limit on range, area of effect, etc... it's wide open.
I'm wondering if others do it 'sandbox' style where everyone at the table works it out.... or... It's a stupendous feat, the rules are wide open, if you make the roll you can do whatever you want.
Also; how about failed feats? Who gets to decide what happens? Sandbox and everyone has a say in it? The opponent who defeated the stupendous roll gets to decide? The player who attempted the feat decides?
Maybe I'm over thinking it and trying to put too much structure on something that is meant to be wild and free. I just don't want a game to end in one turn from a stupendous feat after we spent about 3 hours building stuff =P