your puzzle mode could still be a sandbox but with a starting point and an ending point in the distance (maybe with obstacles between) then assign a point value to every piece the player uses to get from A to B, with grades assigned to total point ranges. best grade goes to the fewest points used
you could use that counter to build a narrative about a brave breakout marble liberating marblekind from oppression by guiding them through your puzzle levels
I AM MARBLECUS!
It’s only five miles this way, but I did swim 1.5 miles this morning, so it all balances out. Also, bonus time with the kid.
Plus, everybody knows that pizza and cookies don’t have calories if you have to run to get them. Well known fact.
I just did the 3.5 miles to grab a slice and met up with my kid who drove there, then rode back home and ran the 1.5 miles to the cookie place for a tea cake, where I again met up with the driving child and rode back to avoid the rain.