Warning: Contains SPOILERS for Sonic the Hedgehog 2
Paramount's Sonic the Hedgehog 2 brings the Master Emerald and the seven Chaos Emeralds to the movies for a power boost to both Sonic and Dr. Robotnik, now sporting a bigger, better Eggman mustache. The Chaos Emeralds were actually housed inside the Master Emerald, which was shattered and subsequently reforged to free said Emeralds, but perhaps the most intriguing detail about the Chaos Emeralds now is the fact that there isn't any clue as to where they have gone. The Chaos Emeralds fly off into the sky after Sonic reverts from his transformation, setting up a major change for the next movie since the powerful emeralds are presumably not on Earth anymore.
Sonic the Hedgehog 2 follows the blue hedgehog on a globetrotting adventure after Jim Carrey's Dr. Robotnik returns to Earth in search of revenge against Sonic (Ben Schwartz). The movie also features the live-action introductions of popular Sonic characters Tails the Fox (Colleen O'Shaughnessey) and Knuckles the Echidna (Idris Elba). Knuckles, initially working with Carrey's newly outfitted Eggman, is in search of the Master Emerald, the location of which has been entrusted to Sonic by his late guardian, Longclaw the Owl. Dr. Robotnik betrays Knuckles and seizes the Master Emerald for himself to create a giant Eggman robot before he is defeated by the combined efforts of Knuckles, Tails, and Sonic using the power of the Chaos Emeralds.
The disappearance of the Chaos Emeralds sets up a major sequel change because it will force Sonic and company out into space. Both Sonic the Hedgehog and its sequel have been road trip movies and a movie set in space would be the perfect opportunity to explore many of the planets that have only been mentioned or shown briefly. After Sonic the Hedgehog 2's surprise ending, if Sonic takes to space to pursue the Chaos Emeralds it'll also be a great place to meet new allies as he looks to face Shadow the Hedgehog in Sonic the Hedgehog 3.
Sonic's adventures have taken him from Green Hills to San Francisco, Siberia and Hawaii. Sonic the Hedgehog 2's Master Emerald message from Longclaw was already a bit of a stretch and with the Guardian Units of Nations (GUN) military organization keeping a close eye on Sonic and friends, perhaps taking a break from Earth isn't such a bad idea. Not only would a sequel in space allow the series to visit any number of foreign locations like Sonic's childhood planet, Tails' home, or even Robotnik's mushroom planet, but it could also cut the human subplots from Sonic the Hedgehog 3.
The series' live-action characters bring a certain charm to the movies, especially James Marsden's small-town cop, Tom Wachowski. But Sonic the Hedgehog 3 should also look to branch out by adding other Sonic mainstays such as Amy Rose, Cream the Rabbit, and or even Rouge the Bat. And while GUN is currently tolerant of Sonic's presence on Earth, they may not be as welcoming if more unfamiliar anthropomorphic animals take refuge on the planet. Sonic will need more than just Knuckles and Tails if GUN plans on unleashing Shadow.
Sonic the Hedgehog 2's box office success has assured a third film in the budding franchise and even a spinoff series for Knuckles the Echidna. With the beginnings of SEGA cinematic universe in the works, the search for the location(s) of the Chaos Emeralds could parallel the MCU's Infinity Saga, as the likeness between the Master Emerald and Infinity Gauntlet has already been drawn. Hopefully, Sonic the Hedgehog 3 makes good on its Chaos Emeralds twist and changes up the series for the better.