This galaxy is available once you have access to the Planet of Trials, which is unlocked by collecting the three Green Stars in levels Luigi under the Saucer, The Secret of Buoy Base and Treasure of the Pyramid. This galaxy appears to be a trickier version of Rolling Green Galaxy.
In this level you need balance on the top of a ball and make your way across tricky narrow paths and moving cogs.
Rolling on the Star Ball
You will need to use motion controls to move the ball around. You can do this in handheld or docked; if you choose to play handheld then you’ll need to tilt the whole Switch console and if you’re using the Joy-Cons or a Pro Controller whilst the Switch is docked, then you tilt and move around with those instead. You can also jump by pressing A/B. You can also brake whilst rolling and bring the ball to a fairly quick stop if you tilt your controller/console inwards (or towards you).
Goombas/Mini Goombas - Goombas will simply run at you and try to damage you by touching Mario. To defeat them, spin attack them then run at them to kick them away, or just jump on their head.
Bob-ombs - Bob-ombs will explode 10 seconds after you’ve picked them up. You can throw them at things to blow them up. Walking Bob-ombs will begin their timer when they spot you. They’ll try to walk towards you to harm you. You can still pick them up and use them to explode things, though.