I think he was from the era when the book was originally written? I'm not terribly sure. Human time periods are different than monster ones.

[Mettaton laughs a little.]

I'm sure you'll do just fine, darling.

[It's not like he has any specific idea of how this should be done but damn if he's not going to pretend like he does. He watches her methodically paint and he watches the bush, wondering if something will start happening this soon. Will something jump out of it? Will they be obliterated instantly by whatever capricious forces run Wonderland?

...It's probably a little late to worry about that now, huh?]

Are all the flowers painted?