The Sega Shop released these 6 tees for Sonic Mania PLUS in the summer of 2018. They're mostly just variants of eachother, but the Plus cast makes for a cool & colorful design. The art here is shaded & Mighty & Ray look really good and classically styled. (even though all the art here is technically neo-classic)
The first tee is the odd one out, and it is called "Tails vs A Chili Dog". Why is he having a fright while holding a food? The art is from the funny, silent Youtube Mania cartoon that was used to promote the game in several short installments.

The characters were simplified with a unique looking funny style. The next design is the Mania Plus cast on blue, gray & white choices. (But why are there 2 blue choices?) The last tee uses the geometric circles/squares 'box art' background, with the logo & Plus cast. Each tee is about 26 dollars in the SegaShop online store. They are all adutls sizes.