What is the expanded 2018 version of Sonic Mania called?

The expanded 2018 version of Sonic Mania is called Sonic Mania Plus.

Sonic Mania Plus is an enhanced edition of Sonic Mania, Sega’s retro-styled platform game released in 2017. Rather than replacing the original game, Plus added new content and was offered both as a retail release and as downloadable content for owners of the original version.

The expansion introduced Mighty the Armadillo and Ray the Flying Squirrel as playable characters. Both originally appeared in the 1993 arcade game SegaSonic the Hedgehog, and each has a distinct ability: Mighty can absorb certain hazards while curled into a ball, while Ray can glide through the air.

Plus also added Encore Mode, which remixes stages and changes the lives system, along with a new pinball bonus stage and expanded multiplayer options. A common mix-up is treating “Sonic Mania Plus” as a separate sequel; it is more accurately an enhanced edition of Sonic Mania.