The Sonic the Hedgehog film franchise has made some wild and fascinating casting choices when it comes to beloved video game characters. Every new adaptation presents a new opportunity to shock the audience with a familiar voice or wow the crowd with an outside-the-box performance.
Metal Sonic was introduced in 1993's Sonic CD, where he swiftly became one of the Blue Blur's most iconic adversaries. As one of the most powerful beings in the franchise, he's often the final boss that good and bad characters are forced to team up to defeat. While the character doesn't always have a voice, when he does, it's an intimidating growl accompanied by a robotic effect. A kids' movie like Sonic the Hedgehog likely wouldn't feature a silent antagonist, so Metal Sonic will likely be fully voiced in the film.
Ryan Drummond
Ryan Drummond is a stage, TV, film, and voice actor who has a variety of small roles in projects of all sizes. The reason he makes an excellent choice for Metal Sonic is that he's already played the role. The most recent and most notable vocal performance as the character comes from 2004's Sonic Heroes. Drummond portrayed the character in that 18-year-old game, but he's stayed in the voice acting industry since then. Drummond also portrayed Sonic from the late 90s to the early 2000s, making his role as Sonic's animatronic equivalent obvious.
Casting the video game voice actor would typically be unheard of in film adaptations, but the franchise has set that example by casting video game voice actor Colleen O'Shaughnessey as Tails. Video game voice actors don't often get their chance at the big screen, but Drummond has appeared in films like Bring it On and Based on a True Story. Drummond would make an excellent Metal Sonic all over again.
Mark Strong
As Dr. Sivana in Shazam! and Frank D'Amico in Kick-Ass, Strong has proven that he makes a stellar villain. As Merlin in the Kingsman films, he portrays an intelligent and level-minded character, always intellectually ahead of his allies and enemies. Strong has an excellent voice, whether in his natural English accent or an adopted American dialect. He always sounds strict, tough, and inherently powerful, based on line delivery alone.
Strong is a solid performer in any role, but as a robotic villain, all of his strengths would be catered to. The high-and-mighty "puny humans" role is a perfect one for Mark Strong's vocal talents, and Metal Sonic is a perfect cartoonishly evil take on that trope.
Thomas Middleditch
The inherent joke of Metal Sonic is that he's a Doppelgänger of Sonic, his equal and opposite. With Ben Schwartz in the role of Sonic, who could be better than Schwartz's longtime improv comedy partner to portray his opposite and enemy? Middleditch might not come across as the traditional villain, but in a comedic action film like the Sonic film franchise, he could be the perfect adversary to Sonic. The two of them would be a perfect pair of nemeses, the chemistry is already there, and the pair already work with flawless back-and-forth, even without a script.
Letting the pair of them riff antagonistic dialogue would add a new level of humor to the studio comedy, creating some jokes that work for the whole family. Middleditch is best known for his role in the HBO series Silicon Valley, but the performer has proven his ability to work in a variety of roles. Letting this comedic duo helm one of the strongest rivalries in genre film history would be a cant-miss plan.
Josh Brolin
The two characters who would likely serve as inspiration for a film version of Metal Sonic would be Avengers: Infinity War's Thanos and Deadpool 2's Cable, so the man who played both roles would be perfect. Brolin has been an actor for around 40 years, so there's hardly any role that fans haven't seen him pull off. As a hero, his stoic confidence and power make him memorable, but he really shines in the villainous roles.
It's hard to imagine the MCU's Thanos having the impact that he had without Brolin's voice behind him. Given the current scale of the Sonic film franchise, Metal Sonic is likely to be a cosmic-level threat, and a little experience in the most famous role of that type makes Josh Brolin a perfect choice.
Vin Diesel
Despite being one of the biggest stars in the world, Diesel is often criticized for his flat emotionless affect. That extremely fair and accurate critique would actually serve as a benefit in the role of a cold killing machine who mercilessly metes out death to all and sundry. Diesel can be a solid performer in the right role, his performance as Riddick is often stellar, especially in Pitch Black. His vocal performance as Groot in the Guardians of the Galaxy franchise is one of the highlights of his career. Diesel is wrapped up in several huge franchises, but he could make a meal out of the Metal Sonic performance.