Dunkey Mode in Sonic Mania
UPDATE: No idea if this was taken out with the Plus update, but as of 7/10/18, it's still on Switch and PC if you download the old version via Steam. You can stop commenting now.
Quick thing I found. Go to Hydrocity, find a hook, mash in Sonic 3 and Knuckles Level Select code, once you hear the ring, go find a boost.
tweez: / neohazard