There are four playable characters in Sonic Superstars at the beginning of the game. But there is a fifth, secret, unlockable character as well, and you can get her just by playing.
Who is secret unlockable character in Sonic Superstars?

Trip the Sungazer is the secret character you're looking for. She has appeared in two previous Sonic titles: Sonic Superstars: Fang's Big Break and Sonic Superstars: Trio of Trouble. In both of these titles, Trip appears in her full armor, and her face is never shown. But Sonic Superstars gives us a glance at what is under that massive helmet of hers.
How to unlock Trip in Sonic Superstars

In order to unlock Trip the Sungazer in Sonic Superstars, all you have to do is complete the story once with any of the four playable characters. After defeating Eggman in the final world, Trip will become a playable character that can be selected on the menu.
- Trip has a wall-climb where she turns into a lizard-like donut that can spin up even the most sheer cliffs.
- When she is in her donut form, Trip's whole body is covered in spikes, which will quickly dispatch any enemies in the way.
- She has a spin dash.
- Trip can also use a double jump.
- Instead of going blonde and invincible like Sonic, Trip turns into a flying, golden dragon-lizard thing who can breathe fire out of her mouth.
She has her own version of the story too, so I highly suggest playing through the whole game again with her and her unique powers.
For more Sonic Superstars, check out All giant ring locations in Sonic Superstars on Pro Game Guides.
 
					 
						 
																								 Mina Smith is freelance writer from Richmond, VA who specializes in video game articles, mostly how-to guides. She has been writing about video games full time since 2019, but started part-time in this career almost a decade. Her number one passion has been video games since the 1990s, and her favorites are FF1, Baten Kaitos, and Viewfinder. In the past five years, Mina has written more than 2,500 articles and has garnered about a quarter of a billion views from audiences all over the world.
						Mina Smith is freelance writer from Richmond, VA who specializes in video game articles, mostly how-to guides. She has been writing about video games full time since 2019, but started part-time in this career almost a decade. Her number one passion has been video games since the 1990s, and her favorites are FF1, Baten Kaitos, and Viewfinder. In the past five years, Mina has written more than 2,500 articles and has garnered about a quarter of a billion views from audiences all over the world.