The Lost Episodes...

Sadly, Sonic Underground's life was cut short, and no further
episodes past 40 were created. It came as a shock to me, and
I felt kind of empty. It's a shame they never finished...but
have faith, everyone knows that no matter what, Sonic, Sonia,
and Manic would have defeated Robotnik, reunited with their
mother, and restored peace back to Mobius.