It's YOUR idea. How do YOU imagine it playing out? Which features of Sonic Mania make the game fun for you? And which features of Hollow Knight make the game fun for you? Where is the overlap? Where is the divergence? Where is the synergy?

Tom Sloper said:

It's YOUR idea. How do YOU imagine it playing out? Which features of Sonic Mania make the game fun for you? And which features of Hollow Knight make the game fun for you? Where is the overlap? Where is the divergence? Where is the synergy?

From a slightly different angle: can you identify what makes Sonic Mania and Hollow Knight special relative to other games in the same genre, or are they just two well made and typical games? If they do have special or extreme features, are they compatible? Example: if you like difficult dodging in a shoot'em up you might appreciate both quality (e.g. Raiden) and quantity (e.g. Dodonpachi), but trying to push both in the same game by covering the screen in fast and smartly aimed bullets would make the game too difficult to be fun.