Tonic the Hedgehog

Tonic the Hedgehog was a spiky, brown hedgehog who claimed to be Sonic the Hedgehog's long-lost brother. Sonic did not remember Tonic (Tonic suggested this was because they were "born at a very young age"), but admitted that Tonic did look the way Sonic once had (before becoming blue and streamlined ). Tonic asked to join the Freedom Fighters, but Sonic refused, saying he didn't trust Tonic, leading Tonic to run away crying.

In fact, the whole affair was a plot by Doctor Robotnik to infiltrate the Freedom Fighters, and Tonic was in fact the shape-shifter Metamorphia. After being discovered contacting Robotnik by Tails, Metamorphia dropped the disguise.