1x12 - Sonic Underground

The Hedgehogs receive a message they believe is from their cousin. In the message, a castle is left to Sonia, who revels in the idea of having a castle for the Underground headquarters. Sonic, Manic and Sonia arrive at the castle only to see an old, dark dilapidated structure. Inside the castle, the Hedgehogs all have separate meetings with a mysterious apparition who resembles their mother.