Well, when it comes to bad memories, this is certainly one of my worst.

[And he hates to admit it.]

Yes. This was part of his plan. Incapacitate me, besmirch my reputation, and then when no one wanted anything more to do with me, return and keep me around like his little toy. He'd have me all to himself.

[He shudders, in both fear and anger at the thought. This is just... this is just ruining everything.]

No point in resisting? Sans, darling, you can't say you know me and think that I wouldn't resist telling the truth to my last dying breath.

[He is made of lies and subterfuge, it's who he is as a person.

When Sans mentions being afraid of Mirrorton, Mettaton frowns.]

I don't want you to be scared of him. He shouldn't be scary. He's me, Sans, my other half, and I want him to be good. It means so much to me. If he can be good, so can I.

[He gives his own sigh, stepping towards Sans.]

I don't want to leave. But you're right. And if I am leaving with you, at least I am leaving in good company.

[It's a lighter truth than how he actually feels, but it's still the truth, and it slides. Mettaton is pretty grateful for that.]