Super Mario Galaxy 2 has 242 stars: 120 regular stars, 120 Green Stars and the two Grandmaster Galaxy missions. Track those groups separately so a story clear is not mistaken for full completion.
First ending and World S
Progress through Worlds 1–6, collect the Grand Stars and defeat Bowser in Bowser’s Galaxy Generator. Continue into World S, clear the remaining regular missions and return for hidden stars, Chimp challenges and Prankster Comets.
Regular-star audit
The first target is 120 genuine Power Stars, including all ordinary hidden and comet missions. Bronze Stars obtained through the Cosmic Guide do not replace the Power Stars required for the full collection. Revisit any Bronze Star mission and complete it yourself.
Unlock the 120 Green Stars
After collecting all 120 regular stars, defeat Bowser again and finish the ending. The Green Star hunt adds two or three numbered stars to every galaxy except Grandmaster. These are positional detours through familiar stages. Listen for the chime and use the exact numbered route in each galaxy chapter.
Comet Medals
Collect the single medal in each galaxy. The original 48 galaxies contain 48 medals; Grandmaster adds the last one. A medal helps unlock the corresponding comet challenge, but additional progression may still be required before the comet appears.
The final two stars
Collect all 240 regular and Green Stars to open Grandmaster Galaxy. Clear The Ultimate Test, take its Comet Medal and meet the Banktoad requirement for The Perfect Run. Complete that one-health-point course to reach the final total of 242.