Trivia: Sonic not being able to swim is a callback to the original video-games, where Sonic can't swim. When he's underwater, he can only movie like normal (albeit slower), and will drown after a brief period. In order to avoid drowning, he has to either surface or make contact with large air-bubbles that he can breathe in. This is also referenced in the movie when Sonic sucks in a giant air-bubble in the temple ruins while he's underwater to avoid drowning.
Trivia: Idris Elba has stated that he pitched the idea of giving Knuckles a high, squeaky voice to humorously contrast with his strength and fierce persona. Thankfully, Elba and the director decided that this idea wouldn't work, and would probably just annoy fans, so they instead settled on a more tough, regal voice.
Trivia: Tails is voiced by Colleen O'Shaughnessey. This is actually notable, as she had previously voiced the character in several video-games and the animated series "Sonic Boom!" She's the only voice actor from the video-games to return to voice her character in the movie series. The rest of the characters are voiced by celebrities.
Trivia: At one point, Knuckles hits Sonic and Sonic drops and loses his bag of rings. This is a subtle reference to the video-games. In the video-games, Sonic collects rings which act as a sort-of surrogate health-meter. When he gets hit, he loses all his rings, and has to recollect them. (If he gets hit again while having no rings, he dies).