The animals you free in the bonus games at the end of Toxic Caves and The Machine include Tails, as well as the supporting cast of "Sonic the Hedgehog" and the Archie comic book: Princess Sally, Boomer/Rotor, Bunnie, and Muttski. The Cluck bots that invade Toxic Caves and Lava Powerhouse are based on Robotnik's mechanical pet, also from the same show. Finally, the chicken bots circling the capsule in The March bonus are based on Scratch, one of Robotnik's incompetent cronies from "The Adventures of Sonic the Hedgehog.
On the final day of Spinball's development, the team was throwing their 'end-of-project' party when the Japanese group working on Sonic the Hedgehog 3 dropped in to see how things turned out. Among the group was Hirokazu Yasuhara, who, upon seeing the start-up sequence, wondered how the Spinball team talked Sega into paying for the rights to the original Sonic theme song. It turns out that the Spinball team was completely unaware that the rights for the original Sonic music belonged to Dreams Come True, who had become quite famous since the music was composed two years prior. Their asking price was more than Sega was willing to pay, so at the very last minute composer Howard Drossin whipped up a new opening jingle which became Spinball's theme.
This was the first (and thus far, only) Sonic game to be developed entirely in the USA.