I recently found an extremely easy way of doing this. I'll put it in a step by step order:
Note: Once the level starts you have to be quick, if you go over 1 minute, pause and hit restart.
1. Get enough Gold/Silver Medallions to unlock Debug Mode.
2. Go into Mania Mode and hover over "No Save" then press
to enter the Secrets Menu and make sure Debug Mode is turned ON, then press OK to exit.
3. Hover back over "No Save" then press and hold
and
until the Level Select screen comes up. Select Stardust Speedway Act 2.
4. In the level, press
to enter Debug Mode and fly all the way to the right to get to the end of the stage.
6. Back track to the Red Spring (dont touch it) and press
until you become a Checkpoint. Then press
to set the Checkpoint on the ground.
7. Press
to return to your character and run through the Checkpoint to activate it.
8. Press
to re-enter Debug Mode and then press
until you become an enemy. Press
to spawn then enemy, then press
to exit Debug Mode.
9. Touch the enemy and let it kill you. (Doing so tells the game you are no longer in Debug Mode and you will respawn at the Checkpoint you just activated. Run straight forward to find Metal Sonic's Hologram and Achievement unlocked.