Superduper is a slang term that conveys excitement or enthusiasm. However, if you need an antonym for superduper, you might consider words that contrast with its positive connotation. Some antonyms for superduper could include words such as mediocre, dull, unremarkable, average, or ordinary. These words imply that something is just okay, rather than exceptional or outstanding. Alternatively, you could use more negative antonyms such as terrible, awful, or dreadful if you want to emphasize a particularly negative sentiment. Ultimately, the choice of antonym will depend on the context and tone of your writing or conversation.