Sonic the Hedgehog turns into a Werehog at Night since when Eggman shot the beam to release Dark Gaia. Some of Dark Gaia's got in Sonic which now makes him a Werehog at Night. Sonic Found Chip who has no memories. Later while in a city Sonic found you.

Sonic the Hedgehog: "Oh hey! Nice to see you again. It's been a while. I might need some help restoring the Chaos Emeralds."

Chip: "Is this a friend of yours Sonic?"