Sonic the Hedgehog: The Movie

Sonic the Hedgehog: The movie was originally a two episode Original Video Animation (OVA) dubbed and distributed by ADV Films as an hour long movie. It appears loosly based on the storyline of Sonic CD and introduces the animated debut of Metal Sonic. The movie is set on the planet Freedom as apposed to Earth or Mobius in other Sonic media

Plot
As Sonic and Tails are relaxing, they get a message from the Presedent of Planet Freedom. They rush to him to find he and his daughter Sara are being held prisoner by Dr Robotnik. The Doctor claims he did this to tell Sonic that in his city of Robotopolis (Not Robotropolis as in SatAm) has been taken over by a robot called Metal Robotnik. Metal Robotnik has set the city's Robot Generator to overload, and it could destroy the whole planet.

(Spoilers) Little does Sonic know, that this is a ruse to lure Sonic down to Robotropolis so that his lifeform data can be sampled to finish Robotnik's latest creation, Hyper Metal Sonic

(End of Spoilers.)