Sonic Mania Plus is an expanded version of Sonic Mania, however features several new modes and items, as well as Ray and Mighty as playable characters along with a new enhanced version of the game called Encore Mode. Also, you can play up to 4 players at the same time on Multiplayer Mode instead of two.
The game will also be released in a proper physical box for PS4, Xbox One and Nintendo Switch. It will come with a deluxe Art Book but if you get it from Japan you can also get it with the Completed Original Soundtrack. The soundtrack on Physical CD in the completed form is currently unavailable anywhere else.
It's due release is July 19 2018. Are you excited?
https://metro.co.uk/2018/07/08/sonic-mania-plus-release-date-pre-order-7680728/
http://www.cdjapan.co.jp/product/HSN-49?s_ssid=e314925b434513f348