Sonic the Hedgehog

Sonic the Hedgehog was a video game. In 1989, Alistair Gordon Lethbridge-Stewart was aware that the main character was a blue hedgehog. (PROSE: Business Unusual) Mel Joseph was playing the game on his computer, completing the Scrap Brain Zone. (PROSE: Conundrum) Mickey Smith had a copy of the game on either his Playstation or Xbox, along with Grand Theft Auto and Gran Turismo. (PROSE: Winner Takes All)

Ace joked with Dr John Watson that whatever the Rakshassi were worshipping, it wasn't Sonic the Hedgehog. (PROSE: All-Consuming Fire) Martha Jones once described the Tenth Doctor's hair as "very Sonic the Hedgehog", although the Doctor said he was going for more of a Sid Vicious vibe. (PROSE: Forever Autumn)

Behind the scenes

 * The Sonic the Hedgehog franchise was one of the many to be featured alongside Doctor Who in LEGO Dimensions. When Sonic and the Doctor are paired together during gameplay, the hedgehog will occasionally enquire about the Doctor allegedly "naming a screwdriver after him".
 * In the real world, the original Sonic the Hedgehog video game was released in 1991. However, the character is implied to have been around from as early as 1989 in the DWU. (PROSE: Business Unusual)
 * Mickey Smith was said to have owned a copy of the game on either his Playstation or Xbox. Assuming he meant the original game, as well as assuming Sonic's game library was indentical between the DWU and the real world, he would've likely owned the game via Sonic Mega Collection Plus, which was released in Europe three months before Winner Takes All, as well as a year before the stories setting.
 * A Sonic the Hedgehog comic series titled Sonic the Comic ran in the UK from 1993-2001. Richard Elson was a prominent illustrator for the series, and Lew Stringer a prominent writer.