We all know that 2005's Shadow The Hedgehog was intended by Sega to be a more mature, darker take on the whole Sonic the Hedgehog universe – but it seems it could have been a lot more M-rated.
Jason Griffith, who voiced the title character, has spoken to GameLuster about working on the game, and reveals that Sega initially wanted an M-rating (thanks, Nintendo Everything):
Back when I was recording for that game, for Shadow the Hedgehog, I don’t remember what year it was, but they sat me down in the studio and they weren’t sure what rating the game was going to get.
They were going for an M-rating with this game and they hadn’t heard back from the agency if they were going to get it yet. So they had me record two takes for every line, and I swear, the version that was for the M-rating, they had me say f*** in every single line. It was just every sentence, I would be yelling ‘Sonic, give me that f***ing Chaos Emerald!’ or something like that. I had no idea what was going on but I just went with it, and I had fun. There’s a hard drive somewhere with hours of recordings of Shadow yelling f*** at Tails and Sonic and stuff.
In the end, Shadow the Hedgehog would gain an E10+ rating from the ESRB due to "mild" profanity and violence, so it still went some way to making the series a little more moody and mature – just not as far as Sega might have done at one point.