A logic puzzle with portals. Choose which portal pair is active and send the rolling marble through the rooms to the exit.
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Rings of the same colour are a pair: in one, out the other. Only one pair works at a time, so tap a ring to choose it, then press GO. You can switch pairs while the marble is rolling.
Walls bounce the marble back, purple mirrors turn it, and dark holes send it back to the start. Alternate routes collect bonus stars; shortcuts skip them.