Sub-Sonic

"Sub-Sonic" is the twelfth episode of the first season of Sonic the Hedgehog (SatAM).

Synopsis
Robotnik and Snively discover an underground oil lake and start drilling, but their robotic snake probes disturb a purple subterranean creature. They also inadvertantly block off a green ungerground stream, forcing the mysterious green water to rise to the surface and flow into the Great River.

Meanwhile, Sally Acorn, Rotor Walrus, and Tails attempt to grow some trees in the area around Knothole, but find that nothing will grow. In fact, even the trees in the Great Forest are dying - Robotnik's pollution is spreading faster than they thought. Elsewhere, Sonic the Hedgehog is fishing at the Great River. A huge fish snags his fishing pole, pulling it - and Sonic himself - into the water. Sonic waterskis behind it for 10 miles (apparently) before being shaken off. When Sonic tries to explain the story to the other Freedom Fighters, he shakes water from his ear onto the withered tree shoots, which suddenly grow very large. Sally decides they must try to get more water from the Great River, and takes Sonic, Rotor and Antoine on a boat to get some. Sonic is impressed by Rotor's boat, although Rotor says he'd rather be a hero than a handyman. Suddenly, the boat is sucked down a whirlpool and spat out in an underground cavern, which seems to have been used as a dumping ground for Robotnik's garbage. As they try to navigate the tunnels, Antoine disappears.

Sonic, Sally, and Rotor row their boat into strange rainbow-coloured water, which suddenly begins to boil and turn pink. They abandon ship just before it sinks, and discover a cavern filled with beautiful plants - some of which have teeth and try to attack. As Sonic ties up the man-eating flowers, Sally disappears just like Antoine. Sonic and Rotor find what seems to be a palace or throne-room, but it is filled with more of Robotnik's trash and there is nobody home. They hear a noise, and Sonic goes to investigate only to be captured by the purple creature from earlier in the episode. Rotor manages to escape by accidentally tripping into a hole. Rotor discovers an even deeper chamber, also filled with plantlife, where a green river has been blocked off by fallen rubble. He unblocks the river - the audience is shown that roots from the Great Forest are fed from the river, and so had been dying while it was blocked off - then collects a sample of the green water in his canteen.

Rotor finds Sonic, Sally, and Antoine, who have been stuck up to their necks in a lake of Robotnik's pollution. He helps Sonic reach a Power Ring, and together they rescue Antoine and Sally. Rotor is hailed as a hero. The four Freedom Fighters again encounter the purple creature, who accuses them of polluting his world and thereby killing all the other members of his species. They explain that Robotnik is really responsible, and that he has polluted their world too. They are attacked by Robotnik's snake probes, and on Rotor's advice Sonic runs up to the surface to deactivate Robotnik's oil platform, which he does.

Underground once more, Rotor uses the green water sample to turn the oil lake into clean water. Although there is not enough water to save the Great Forest, their new purple friend gives them something that could help - and Sonic offers to take him fishing any time.

On the surface, Sally uses the remaining green water on their tree shoots, which begin to thrive. Rotor admits that being a hero is exhausting, and that from now on he'll stick to being a handyman.