The phrase "more mumpish" is a bit obscure, and therefore finding antonyms to it can be a bit challenging. However, we can look at the individual words "more" and "mumpish" to find their respective antonyms. "More" has antonyms such as "less," "fewer," and "reduced." Whereas "mumpish" means sullen or gloomy, so its antonyms can include "cheerful," "uplifting," and "optimistic." So, if we are to find antonyms for the phrase "more mumpish," we can use combinations of these antonyms to create phrases such as "less gloomy" or "more cheerful and optimistic.