So the plot of Marble Madness is basically Steven and CGs trying to figure out of where Plug Robonoids are coming but however Marble Madness would have been a different episode
Ben Levin reveal this episode went through 2 MAJOR REWRITES during the outlining stage
The original idea was that Steven would end up trapped with one of the Robonoid and befriended it, but it was decided this was too similar to the plot of the previous episodes "Steven's Lion" and "Monster Buddies".
The second outline was about a single Robonoid breaking when it landed on Earth, being repaired by the Crystal Gems to follow it, and Steven following along in secret when the other don't let him come with. It was decided this didn't have much going on at the start and that Steven being kept out of the mission didn't make sense.
The final draft was written with a series of Robonoids dropping onto Earth and the whole team, Steven included, following one they allow to land safely. Yes this is the one we got!