Super Smash Bros. director Masahiro Sakurai describes the above screenshot thus: “The ropes surrounding the ring. You can actually use the stretchiness of the ropes to do a spring jump. However, you can’t pull on them to launch yourself sideways in a lariat attack though.”
Alongside the screenshot above, Sakurai also posted the other screenshots you see below to the game’s official website last week. Alongside the screenshot featuring Rainbow Road, Sakurai stated: “Watch out for the Shy Guys driving down Rainbow Road.”
It looks like those will be stage hazards on the Rainbow Road stage, at least on 3DS.