One of the older Sonic The Hedgehog series, Sonic Underground is where Sonic goes out with his two siblings(only featured in this, OTHER then fan-made videos and clips) Sonia and Manic, and they go out to find their lost mother, who has been hiding from Robotnik, the badguy.
Characters
Really strangely, Knuckles the Echidna appears in a classic Sonic series! And this is the only classic Sonic series Tails isn't in.
