Unfortunate I’m not able to participate this time, but I still might help with some ideas:

A runner with the goal to go around a planet. The view gradually becomes upside down halfway through (like Australia)

You’re stuck in a small house full of secrets. Your goal is to get out only to find out the outside is just a bigger house

A cool mechanic would be to start in a small world that keeps growing (borders moving out) as you explore and find stuff.

You control a spaceship in a big cluster of small planets. You carefully land on them to refuel/get food. Gravity rules apply

Also I tweet ideas @73lion123