No Export for You: Inverted? The last season only aired outside Japan, despite a full Japanese voice track being produced.
The Other Darrin: Unlike the games in 2003, the Anime featured different voice actors from the 4Kids line up such as Jason Griffith as Sonic and Shadow, Amy Palant as Tails, Dan Green as Knuckles, Lisa Ortiz as Amy, and Mike Pollock as Dr Eggman. They would later replace the game voices as the official voice cast until 2010, when all but Mike Pollock would be replaced with the current voice cast.
From the same episode as E-90 Super Sweeper (aka Thunderbird 2), the launch sequence for the new X-Tornado (the collapsible palm trees) is also a shout-out to Thunderbird 2's launch sequence from the puppet series.
Mothra and MOGUERA appear in Episode 48 on a mysterious island. Mothra's a bit more vicious-looking and antagonistic (a nod to her dark twin Battra) and MOGUERA is based on his Showa appearance and battles Sonic, Knuckles and Rouge at the climax of the episode. Godzilla also appears as a statue that Bokkun sits on for a minute before it crumbles apart when MOGUERA appears.