What engine did Christian Whitehead use for Sonic Mania?

Christian Whitehead used the Retro Engine for Sonic Mania.

The Retro Engine is a custom 2D game engine created by Whitehead and used for Sonic Mania, the 2017 Sonic title developed with Headcannon and PagodaWest Games. It was designed around the visual and technical style of classic 32-bit-era games, emphasizing raster graphics, sprite work, and palette manipulation rather than a conventional 3D framework.

Whitehead first created the engine for his 2007 fan game Retro Sonic. Its capabilities helped him produce a proof-of-concept Sonic CD remake, which eventually led Sega to commission official mobile remasters of classic Sonic games. That history made the engine a natural fit for Sonic Mania's modern recreation of the Genesis-era style.

The main confusion is between the Retro Engine and Sega's Hedgehog Engine. The latter powered several later 3D Sonic games, while Unity and Unreal Engine are general-purpose commercial engines. Sonic Mania's retro presentation was not merely a visual filter; it was built using technology tailored to 2D Sonic gameplay.