[Toriel finally managed to calm down and, after chuckling one last time, she moved a bit closer to get his signature. And, of course, a motherly being like her can't help but show joy and excitement... because- look at that kid, he looks so proud of himself!]

Steven, mh? That's a wonderful name, young one. I am Toriel. And if you think I have a great sense of humor you should meet my friend, Sans. [Her... best friend, maybe?] I'm sure he'd be a worthy opponent for you in a joke-challenge.

[And she holds the signature close to her heart, smiling]

Thank you, my dear, I will treasure it.