FakeMrM

This is not his dream body.

Still Famous and Beloved by all, albeit at the expense of his own sanity

I imagine he's learned to feign his confidence very well.

He's stuck having a menacing smile, even when he doesn't want to.

Under what eventually became a false promise by Alphys that he'd get his dream body after he helps her convince Asgore to allow her to become the Royal Scientist.

Alphys purposefully chooses to make Mettaton EX his least desirable body in favor of creating a body that is dangerous in both design and power. The Neo body would still be her greatest creation.

Alphys forced program his body to malfunction at any emotional implications of remorse, concern, and defiance.

Hence why he has an extra pair of arms built into his body that she can control. Juuuuuust in case he manages to override the program.

Just like his own experience with being given a false sense of friendship and promises, he does this to Frisk by reassuring them he's on their side. Then betraying them.

Even more dramatic, he swoons, and giggles.

The only way I can describe how he moves and carries himself would be just like Jessica Rabbit. Slow and Intentional, please see my vision.

Instead of saying "Oh yes" in his EX intro, he says " Daaarrrrliiiingggg~"

He can retract his extra arms, Alphys can also bring them out.