I don’t normally do weight gain art involving robots (unless commissioned). It just feels weird for me cuz metal isn’t expandable and robots don’t eat food. But since the robots in Undertale are also made with magic and Mettaton has his own cooking show, it makes more sense to me in this scenario.

I also headcanon Mettaton as being very bottom heavy. Gotta have a nice ass to go with those nice legs, amirite?