Watch Sonic the Hedgehog 2 Full Movie Free Online 123Movies. After settling in Green Hills, Sonic is eager to prove he has what it takes to be a true hero. His test comes when Dr. Robotnik returns, this time with a new partner, Knuckles, in search for an emerald that has the power to destroy civilizations. Sonic teams up with his own sidekick, Tails, and together they embark on a globe-trotting journey to find the emerald before it falls into the wrong hands.