"Retro" style continues to presist.
This was available about 2 years ago from TopHeavy, however you may still see it around today, depending where you go. Again, 'wacky retro' this time featuring cartoony Robotnik being chased by spinning stock-art Sonic. Despite being 'loud' yellow and green, the design is rather well thought out, with rings in the background and wavy text. It maintains a look of something 60s or 70s-ish.
Confirmation by SegaSonic01.
Is this official or not?
Interestingly enough, it is. This shirt used to be on the "Bootleg" page due to it's...lack of design. The design is plain and 'wacky retro' which is currently hot in officially licensed items...but really, not a whole lot of effort went into this. The oldest stalest stock art, with only black ink and a block font. It looks like it might of been turned out in a garage...but perhaps that's the point! Confirmation by SegaSonic01.