Jim Carrey has proven over the years that he's a master of improvisation. He is, after all, part of one of the best improvised moments in movie history. Flashback to "Dumb and Dumber," when Harry and Lloyd were scripted to get on the hitman's nerves. The comically gifted Carrey then walked up to the plate, swung for the fences, and created "the most annoying sound in the world."
To that end, it's no surprise that Carrey improvised much of his role in "Sonic the Hedgehog." Carrey discussed his improv chops with ComicBook.com. "I'm a big proponent of working it and working it and working it, and coming in with 20 ideas," Carrey said, "and the director will go, 'Just throw them out, see what happens.'" Though some actors are trained to stick to the script, at all costs, Carrey seemingly does his best work when he adds a dash of spontaneity to his lines.
In an interview with The Illuminerdi, "Sonic the Hedgehog" writers Pat Casey and Josh Miller talked about how the Robotnik character was defined by Carrey. "That's why it's difficult to imagine anyone else doing it, because we definitely had [conversations while writing the script] was how funny versus how intimidating do we make him," Miller said. "But Jim really perfectly straddled that. He's like, an intense guy so he's got that good crazy villain focus. But then he's the funniest guy in the world."
Casey also recalled Carrey's ability to make the character uniquely his own. "There was a thing, where people at the studio would ask 'do we make him funny, does that take away from him being intimidating?' It's not one-versus-the-other, it's possible to be both at once if you have a performer that can do that." Casey also said that Carrey had the ability to reason with Robotnik, a villain through and through, and understand why the vulnerable character acted the way he did.
If you had someone as talented, charismatic, and hilarious as Carrey in your film, you'd be wise to let him run with the role and allow him to do his magic.