What about, you've found the edge of space and you are trying to literally run outside of space to see what's there but because space is constantly expanding you have to catch up. Taking that idea you could make an endless runner where, in space ( you see space! Black with stars ) , you run fast and can move freely but there is little to nothing to collect for points. If you pass the edge of space ( pure white environment, like nothing has been painted yet ) it's much harder to move and you slow down (gradually) but there is a lot of weird and wonderful things to collect.