In terms of human characters, it is expected both James Marsden and Tika Sumpter will return as Tom and Maddie Wachowski, Sonic's human family.

Source: https://screenrant.com/sonic-hedgehog-3-news-updates-cast-story/

Sonic's best friend Tails is once again playable in Sonic Superstars, and fans might wish to know how he feels up against games like Sonic Frontiers.

Source: https://gamerant.com/sonic-superstars-origins-frontiers-tails/

Spawn's only in the comic for a brief moment, as he flat out ignores Sonic's pleas for help.

Source: https://www.cbr.com/spawn-greatest-comic-book-crossovers/

While that may be true, Sonic's newest blast from the past doesn't have to be stuck in the 1990s.

Source: https://www.cbr.com/sonic-hedgehog-superstars-best-2d-game/

With Sonic's sales matching its reputation, selling a lowly 234,000 units in its first week, Sega had no choice but to make a change.

Source: https://www.cbr.com/murder-of-sonic-the-hedgehog-fandom-success-sega/