"An obvious problem here is that, despite introducing Metal Sonic, the mid-credits scene already shows that he is easily beaten. Amy Rose quickly rescues Sonic from a whole army of Metal Sonics. She takes out a large group with one heavy attack from her high-tech mallet, and then she scrubs off one more with a second hit. Sonic looks like he could have dealt with the first one who attacked him. If the plan is for Metal Sonic to be the villain in Sonic the Hedgehog 4, the mid-credits scene already exposes him as an easily dispatched threat.

It will be difficult for Metal Sonic to be a very compelling villain on his own now. Not to mention, the Robotniks are likely out of the picture after the events of Sonic the Hedgehog 3. Gerald Robotnik (Jim Carrey) disintegrated near the end of the movie, and it appears that Dr. Ivo Robotnik (also Carrey) perished with the destruction of the Eclipse Laser. That means Sonic the Hedgehog 4 will likely need another villain or mastermind to round things out, considering how Metal Sonic was already measured and defeated in the mid-credits sequence."

....

"A villain such as Neo Metal Sonic would be a great move for the franchise. It would provide a refreshing change of pace, utilize a popular villain from the game series, and offer an intense new challenge for Sonic and his allies. Even if this is not the end of Dr. Ivo Robotnik, the character could use a bit of a break right now, especially after how things ended for him in the last movie. Neo Metal Sonic is one of the few standalone villains the franchise could use from the games. However, part of Neo Metal Sonic's backstory still has a Robotnik connection, so the character could still appear to some degree. That said, the plans for the villain in Sonic the Hedgehog 4 remain to be seen..."

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