* CreatorBacklash: Ben Hurst disliked the premise and had a bad time working with the material of other staff, as well as being pitched in favor of a ''WestesternAnimation/SonicSatAM'' continuation.
* CrossDressingVoices: Jaleel White voices Sonia using a modified [[Series/FamilyMatters Urkel voice]].
* FanNickname: Some people call an overpowered Emerald fused Dingo "Chaos Dingo".
* NonSingingVoice: All three hedgehogs had three separate voice actors for the singing segments - Creator/SamuelVincent for Sonic, Tyley Ross for Manic, and Louise Vallance for Sonia.
* RecycledScript:
** The episode "Winner Fakes All" has the same plot as the ''WesternAnimation/SonicSatAM'' episode "Sonic Racer", and "Sonic Tonic" is a rehash of the ''WesternAnimation/AdventuresOfSonicTheHedgehog'' episode "Full-Tilt Tails".
** "Moby Deep" is recycled from ''Series/TheSuperMarioBrosSuperShow'' episode "20,000 Koopas Under the Sea".
** ''Underground'' wasn't afraid to recycle its own plots either; "the hedgehogs meet a foe pretending to be a friend who ends up being a friend" could describe at least five different episodes.
* TalkingToHimself: Jaleel White voices ''all three'' main characters.
* WhatCouldHaveBeen:
** More episodes of this show were planned, but never went beyond the planning stages. Ian Flynn, head writer of ''ComicBook/ArchieComicsSonicTheHedgehog'', stated that he wanted to write a conclusion in comic form (helped by the fact that the cartoon was established to be in the comic series' {{Multiverse}} in an earlier story), but ExecutiveMeddling ultimately prevented this.
** Early concept art shows Queen Aleena with a [[https://www.sonicstadium.org/2012/07/freak-out-friday-the-original-sonic-underground-concept/ very different design]].
** According to Ben Hurst, this series would have at one point been a continuation of ''WesternAnimation/SonicSatAM''. Instead, it was decided to retool the concept and make it into a separate series.
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