Sonic Superstars' pre-order content seemingly indicates that Dr. Robotnik, also known as Eggman, will be a playable character in the game.
Sonic Superstars was first revealed over the course of Summer Games Fest as being a new 2D title in the Sonic series, with multiple playable characters including Sonic the Hedgehog, Miles 'Tails' Prower, Knuckles the Echidna, and Amy Rose. However, a skin that is part of a pre-order package for Sonic Superstars seems to indicate that you can also play as Eggman, with a LEGO Eggman skin available for the game.
This wouldn't be the first time that Eggman was a playable character in a Sonic game. The Sonic Adventure games featured the villain as a playable character, allowing you to see his perspective in the grand scheme of things. Not only does this suggest he's back as a playable character, but it also suggests that the entire cast may be getting a LEGO skin variant of themselves that looks somewhat similar to their Minifigures.