Sonic and Tails were playable in the prototype for Knuckles' Chaotix and that was called Sonic Crackers. Heavy and Bomb were one the first original Chaotix, but why did they come? Let's find out! Well first of all when your chosing your partner they have statuetts that are the the colors of the character, but slightly changed. Heavy's colors are blue, which is Sonic's color, and Bomb's colors are yellow, which is Tails' colors. Second is that in the good ending, it shows Sonic and Tails on the Tornado in the backround with the Chaotix, which could possibly mean that Heavy and Bomb replaced Sonic and Tails in the game. As you can see by this image:


If you agree or do not agree with me, please put your most honest opinion in the comment section *slow-mo* below.