Similarly to the case of Blade, Blue also originates from the Sonic fan characters created by Newgrounds user, Equinox-Twilight, particularly derivating from the other fan character Flare the Hedgehog (said to be the "brother" of Sonic the Hedgehog) who mainly appeared in the KA Omake Flash animated series. User topcat13 was also in charge of redesigning Blue to be completely unique especifically for the game, so he could be told apart from Flare; the name "Blue" may have been also be thought up by topcat13 himself, but this is not confirmed. Something that has never been clarified is whether or not Blue was intended to be in the game that eventually became Super Smash Flash, which was not initially projected to be a Super Smash Bros. fan game but as a platformer action-oriented game starring Blade. This also makes Blue's relationship with Blade a full mystery or even if they are supposed to be related at all. Blue's ultimate design came after Super Smash Flash was finally completed and released to public: he is a blue hedgehog with loose but long quills who wears red gloves and shoes with black accents and who wields a characteristic sword; much like characters in the Sonic canon, he is able to use the Spin Dash and the Spin Jump.
Blue debuts as a playable character in the original Super Smash Flash as a clone of Blade. His attacks are slightly more powerful than Blade's as the cost of speed. The fact he was made specifically for the game could mean Blue was projected to accompany Blade, but no word exists to confirm this, so why he stayed after Super Smash Flash become a Super Smash Bros. fan game is unknown.
In Super Smash Flash 2
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The subject was never implemented into the game or was removed, cut or altered at some point of its development, and this article pertains to its original implementation.
Blue was previously confirmed to appear again in Super Smash Flash 2, coming with a new redesign (as seen on the right) but with some similarities to his Super Smash Flash counterpart. He would have more pronounced fiery attacks. However, in May 18, 2012, was announced that he would be removed from the roster, along with Blade and other fan characters.
Blue's sword seems to be a flamberg-type rapier. Note the hand shield under his right hand. This "Flamberg" somewhat emits fire, much like Blade's own katana, which emits electricity.