Sonic & Sega All Star Racing Easter Egg - Mobi Deep

In the Sonic the Hedgehog stage titled "Ocean Ruins," there will be a point where you go in the first tube (tunnel) with water around you. Focus on the left side of the tube and you should see a whale just before the second dash panel. This is Mobi Deep from Sonic Undergroud who makes friends with classic Sonic. Not to mention Sonia (classic sonic's sister) is in Roulette road as well who is also a Sonic Underground character.