Merlina's theme is a sad piano remix of the Final Boss theme "With Me".

The music that plays during the fan art gallery is a Violin Remix of the song "It Doesn't Matter", Sonic's theme (Sonic Adventure 2 version).

Sega held a competition for fan artwork of Sonic characters. The top twenty of the US, Europe and Japan were placed in the game for display and their artists would win a free copy of the game. However, one of the winning entries submitted by Italian artist Antonino Miniero was discovered to actually be a replica of a piece of fan art by artist Mega777. Miniero was disqualified by Sega of Europe and did not receive a copy of the game, and later issued a full apology on the Sonic Italia message boards stating:

To promote the release of Sonic and the Black Knight, Neopets released a browser game called "Sonic Knight in Training", where Sonic must use Caliburn to deflect apples shot at him from the three Knights of the Round Table (Lancelot, Gawain, and Percival). If the player received a high enough score, they would unlock a then-new trailer for the game.

Tommy Tallarico, credited composer for the "Molten Mine", "The Cauldron", and "Great Megalith" music tracks in Sonic and the Black Knight claimed in 2022 to have been the first American to work on the Sonic the Hedgehog video game series. Even if one refuses to count external work such as localization, marketing, and multimedia adaptations, this is not true, as Americans have worked on art, programming, and music for Sonic titles as far back as the 16-bit version of Sonic the Hedgehog 2, with Tallarico having previously shown awareness in 2014 of American pop star Michael Jackson's involvement in creating music for Sonic the Hedgehog 3. In 2023, his involvement in writing the three tracks came into question when it was discovered that they contained similarities to several demos originally credited to Todd Dennis, a composer at Tommy Tallerico Studios in the 1990's, and originally written for the games Black Dawn and Adrenix.

Sonic has unused voice clips for when using the Gale Drive move, which can be heard in both English and Japanese.