While Metal Sonic is a prominent character in the game, and the game itself uses a lot of visual effects, holograms were not a feature of the game.
It's possible you might be thinking of another Sonic game, or perhaps a fan-made creation.
Could you provide more context about what you're looking for? For example:
* What specific part of the game are you thinking about?
* Is there a specific scene you're recalling?
* Do you remember any other details about the hologram?
With more information, I can help you figure out what you're remembering!