Gravity Guy

I would highly recommend making this your second to last achievement in the game, with the following being your last:

Also make sure you have this achievement before going for Moon walk:

The reason why is because you will get Moon walk before playing for 10 hours if you are using the save trick for your run-throughs, and this will count towards the 10 hours anyway. Gravity Master will also involve running which will count towards Moon walk.

Play either the Run or Rescue missions, and get to a checkpoint where you will fall off and die after running for a bit (rather than having it slope up). Your first opportunity for this is after the first checkpoint. Alternatively you can get to a further checkpoint where there are speed arrows and/or a longer path before falling.

The game will automatically respawn you at the previous checkpoint, however, make sure that you click "no" when it asks you whether you want to use a slow motion. The game will ask you generally 3-5 times before continuing without asking. Check back every 10 minutes or so until you are comfortable that it will no longer ask you and then go have lunch, watch a movie, or let it sit overnight. To be on the safe side, you can download the auto-clicker as mentioned in the solution for Gravity Master linked above, to ensure the game doesn't stop you with questions.

NOTE: make sure your computer is plugged in (if you have a portable) and is NOT set to sleep, hibernate, or screen saver after a certain amount of idle time.

Do NOT do this in practice mode as many of the achievements cannot be earned there, and it's not worth risking it for this one.

I ran the Perfect Run and Perfect Rescue missions using the save trick, so this achievement took me over 5 hours of idle boosting to get after finishing the missions. You can find the save trick method in these solutions:

Solution for Perfect Run In Gravity Guy (Windows)
Solution for Perfect Rescue In Gravity Guy (Windows)

Please let me know if you have questions.